Star polymer nanoshells and methods of preparation thereof

ABSTRACT

A nanoshell is disclosed, comprising a star polymer occlusion complex comprising i) an amphiphilic unimolecular star polymer having a crosslinked core covalently linked to 6 or more independent polymer arms, and ii) a cargo material occluded in the star polymer; and a shell comprising an inorganic material in contact with a peripheral surface of the star polymer occlusion complex.

This invention was made with Government support under Agreement No.H94003-08-2-0806, awarded by the Defense Microelectronics Activity,effective Sep. 12, 2008. The Government has certain rights in thisinvention.

PARTIES TO A JOINT STUDY AGREEMENT

This invention was made under a joint study agreement betweenInternational Business Machines Corporation and San Jose StateUniversity Research Foundation.

BACKGROUND

The present invention relates to star polymer nanoshells and methods ofpreparation thereof, and more specifically to star polymers comprisinggold, silica, or iron oxide in a peripheral shell, and a cargo materialoccluded in a core region of the star polymer.

Recently, nanoparticles of increasingly complex composition, structureand function have been developed for a wide range of applications suchas bio-sensing, drug delivery, intracellular imaging and therapeutics.These include, for example, organic nanoparticles such as dendrimers,inorganic nanoparticles such as silica or transition metal-containingnanoparticles and nanoparticles comprised of composite materials.However, it is a challenge to construct structurally complex inorganicnanoparticles having an average particle diameter below 100 nanometers,and a low polydispersity.

Deposition of silica onto small nanoparticle templates has been used toproduce nanoscale core shell structures. Templates include goldnanoparticles, inorganic quantum dots, or organic polymers to producecore shell structures, but nucleation sites must be incorporated ontothe surface of these templates for the silica to grow and any opticalproperties produced are constrained to those of the nucleating template.

Additional methods and materials are needed for preparing nanoparticlescomprising silicon and/or other inorganic materials, including metals.

SUMMARY

Accordingly, a nanoshell is disclosed, comprising:

a star polymer occlusion complex comprising i) an amphiphilicunimolecular star polymer having a crosslinked core covalently linked to6 or more independent polymer arms, and ii) a cargo material occluded inthe star polymer; and

a shell comprising an inorganic material in contact with a peripheralsurface of the star polymer occlusion complex.

A method is disclosed, comprising:

forming a mixture of an amphiphilic unimolecular star polymer and acargo material in a first solvent, the star polymer having a crosslinkedcore covalently linked to 6 or more independent polymer arms;

injecting the mixture into a second solvent, the second solvent being anon-solvent for the cargo material, thereby forming a star polymerocclusion complex, the star polymer occlusion complex comprising thecargo material occluded in the star polymer; and

depositing a shell-forming inorganic material on a peripheral surface ofthe star polymer occlusion complex using one or more sequentialprocesses, thereby forming a nanoshell comprising a shell, the shellcomprising one or more inorganic shell layers.

Another method is disclosed, comprising:

forming a mixture containing an amphiphilic unimolecular star polymer, acargo material, and iron oxide nanoparticles in a suitable solvent, thestar polymer having a crosslinked core covalently linked to 6 or moreindependent polymer arms; and

injecting the mixture into a second solvent, the second solvent being anon-solvent for the cargo material, thereby forming a nanoshellcomprising the star polymer, the cargo material, and the iron oxideparticles.

Also disclosed is an aqueous mixture comprising the above-describednanoshell.

Also disclosed is a method of diagnostic imaging, comprising contactinga cell with the above-described aqueous mixture.

The above-described and other features and advantages of the presentinvention will be appreciated and understood by those skilled in the artfrom the following detailed description, drawings, and appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a three-dimensional drawing representation of a unimolecularstar polymer.

FIG. 1B is a graphical layer diagram illustrating the hydrophilic andhydrophobic sub-regions of an exemplary star polymer.

FIG. 1C is a three-dimensional drawing representation of an exemplarystar polymer occlusion complex, comprising three occluded particles ormolecules. The occluded material can be a pharmaceutical agent, imagecontrast agent, chromophore or material selected to form an occlusioncomplex having a desired dielectric constant.

FIG. 1D is a three-dimensional drawing representation of an exemplarystar polymer nanoshell comprising a contiguous peripheral shell disposedon a star polymer occlusion complex. A portion of the shell has beenremoved to reveal the contained star polymer occlusion complex.

FIG. 1E is a three-dimensional drawing representation of an exemplarystar polymer nanoshell comprising a porous peripheral shell.

FIG. 1F is a three-dimensional drawing representation of an exemplarystar polymer nanoshell comprising a non-contiguous shell comprised ofindependent inorganic nanoparticles dispersed in the peripheralinterstitial spaces of a star polymer occlusion complex.

FIG. 1G is a three-dimensional drawing representation of an exemplarystar polymer nanoshell comprising a shell that encompasses more than onemacromolecule of a star polymer occlusion complex. Each star polymerocclusion complex is an independent macromolecular structure.

FIG. 2 is a schematic reaction diagram for the preparation of silicananoshells, iron oxide nanoshells, and gold nanoshells from a commonstar polymer occlusion complex.

FIG. 3 is a photograph of three vials containing (from the left), starpolymer SP-1 (aqueous solution), porphyrin dye (DTBP) (aqueoussuspension), and a star polymer occlusion complex (OC-1) prepared fromSP-1 and DTBP (aqueous solution).

FIG. 4A is a scanning electron micrograph (SEM) of commerciallyavailable solid gold nanoparticles (110 nm). The inset picture is anaqueous solution of the solid gold particles. The solution has a magentahue.

FIG. 4B is an SEM of similar sized (110 nm) gold nanoshells AuNS-1prepared from a star polymer occlusion complex, OC-1, comprisingporphyrin dye DTBP. A drawing representation of the gold nanoshellsAuNS-1 is shown below the SEM, showing the shell encompassing multipleindependent macromolecules of star polymer occlusion complex OC-1. Theinset picture is an aqueous solution of the gold nanoshells AuNS-1. Thesolution has a blue black hue.

FIG. 4C is a graph of UV-VIS absorption spectra of commerciallyavailable solid gold nanoparticles (110 nm) versus similar sized goldnanoshells AuNS-1 prepared from star polymer occlusion complex OC-1.Only the gold nanoshells AuNS-1 absorb strongly in the “biologicalwindow” (ca. 650 nm to 950 nm).

FIG. 5A is a set of four SEMs showing how variation of the goldnanoshell thickness affects the absorbance maxima of gold nanoshellsAuNS-1 to AuNS-4. The thickness varies in response to the ratio of thevolume of the gold seeded star polymer solution to the volume of thehydroxylamine solution added, the total volume and/or reagentconcentration of the growth solution, and/or the addition rate of thegrowth solution to the solution of the seeded star polymer occlusioncomplex.

FIG. 5B is a graph containing visible-near infrared (VIS-NIR) absorptioncurves of gold nanoshells AuNS-1 to AuNS-4, which show a red shift inthe absorbance with increasing particle size.

FIG. 5C is a photograph of four aqueous solutions of gold nanoshellsAuNS-1 to AuNS-4. The hue shifts from magenta-purple on the left toblue-black on the right.

FIG. 5D is a three-dimensional drawing representation of AuNS-5 formedfrom contacting the surface of AuNS-1 with thiol-functionalizedpoly(ethylene glycol) (PEG).

FIG. 5E is a photograph of vials containing AuNS-5 as (left) alyophilized powder and (right) as an aqueous solution. Both the solutionand the powder have a blue hue.

FIG. 6A is a reaction diagram using three-dimensional drawingrepresentations of the star polymer occlusion complex, which shows thenanoshell size (and hence properties) can be controlled by pH mediatedaggregation of the star polymer occlusion complex. The size of theaggregate is a function of pH and/or solvent strength.

FIG. 6B is a set of three SEMs of gold nanoshells AuNS-6, AuNS-7, andAuNS-1 prepared at pH 3.18 (average particle size 50 nm), 8.4 (averageparticle size 80 nm), and 11.3 (average particle size 110 nm),respectively.

FIG. 7 is a set of three SEMs showing the effect of amine monomer(DMAEMA) content of the star polymer on the respective size anduniformity of gold nanoshells. Star polymers SP-1, SP-2 and SP-3 (Table7) were used to prepare star polymer occlusion complexes OC-1, OC-2 andOC-3, respectively. OC-1, OC-2 and OC-3 were used to prepare goldnanoshells AuNS-1, AuNS-8, and AuNS-9, respectively, under otherwiseidentical reaction conditions. The star polymers templates have similarparticles sizes (18 nm to 22 nm), but the resulting gold nanoshells haveaverage particle sizes that vary greatly, increasing with amine contentof the star polymer template.

FIG. 8A is an electron energy loss spectrum (EELS) of AuNS-1 showing thepresence of carbon, oxygen and gold in the sample.

FIG. 8B is a bright field transmission electron micrograph (BF-TEM)showing the nodulous surface topography of AuNS-1 in greatermagnification.

FIG. 8C is a high angle annular dark field micrograph obtained with ascanning transmission electron microscope (HAADF-STEM) of AuNS-1, whichprovides another topographical view of the AuNS-1 surface. The noduleshave a diameter of about 18 nm and are spaced about 16 nm.

FIG. 8D is a cross-sectional scanning electron micrograph of AuNS-1(cross-sectional sample produced using focusing ion beam (FIB) milling).

FIG. 9A is a graph showing the UV-VIS absorption spectra of star polymerocclusion complex OC-1 (single peak at 423 nm in water) and goldnanoshell AuNS-1 (peaks at 419 nm and 790 nm in water). OC-1 isrepresented by the three-dimensional drawing representation. OC-1contains occluded porphyrin dye DTBP.

FIG. 9B is a graph comparing the fluorescence emission spectra of watersolutions of OC-1 and gold nanoshell AuNS-1 for 420 nm excitation. Thefluorescence of the occluded dye DTBP in the star polymer occlusioncomplex (lower curve) is similar to the fluorescence of the occluded dyeDTBP in the gold nanoshell (upper curve). The dye is substantially in anon-aggregated state in the star polymer occlusion complex and the goldnanoshell.

FIG. 10A is a schematic reaction diagram using three-dimensional drawingrepresentations of the “Two-Pot” method of forming silica nanoshells.

FIG. 10B is a schematic reaction diagram using three-dimensional drawingrepresentations of the “One-Pot” method of forming silica nanoshells.

FIG. 10C is an atomic force microscope image (AFM) of the star polymerocclusion complex OC-4 (Z=10 nm) used in the preparation of silicananoshells SiNS-1, using the “two-pot” method.

FIG. 10D is a transmission electron microscope image (TEM) of silicananoshells SiNS-1.

FIG. 10E is a TEM of comparison solid silica particles formed by the“two-pot” method without star polymer occlusion complex.

FIG. 10F is a TEM of the silica nanoshells SINS-2, formed by the“one-pot” method.

FIGS. 11A to 11D are a set of four TEMs of silica nanoshells SINS-3(D_(ave)=25 nm), SiNS-4 (D_(ave)=50 nm), SiNS-5 (D_(ave)=75 nm), andSiNS-6 (D_(ave)=100 nm), respectively, showing size control of silicananoshells can be controlled through coating time, coating reagentconcentration, and/or template size (mixed examples derived from varyingthese parameters are shown). The 25 nm particles were produced using thetwo-pot method. The 50 nm, 75 nm, and 100 nm particles were producedusing the one pot method with extended reaction time and increasingamounts of ammonia in the reaction solution.

FIG. 12A is a schematic reaction diagram using three-dimensional drawingrepresentations of the surface functionalization using organic taggingagents of silica nanoshell SiNS-2 that contains active primary aminesurface groups. Four tagged silica nanoshells SINS-7 to SiNS-10(Examples 17 to 20) were formed using four different molecular weightalpha-methoxy-omega-carboxylic acid succinimidyl ester poly(ethyleneglycol) as organic tagging agents. These are also referred to asPEGylating agents, which comprise a poly(ethylene glycol) (PEG) having areactive succinimidyl ester end group, and are represented as“NHS-Ester-(PEG).” in FIG. 12A. Dansyl chloride dye in FIG. 12A isanother example of an organic tagging agent, serving as a representativecellular targeting agent. This demonstrates the nanoshell surface can bemodified using one or more surface functionalizing agents to form one ormore functionally different reactive surface groups.

FIG. 12B is a graph comparing the UV-VIS absorbance of tagged silicananoshells SiNS-7, SiNS-8, SiNS-9, and SiNS-10. SiNS-7, being fullycovered by the smallest (least sterically demanding) PEG chain, isunable to react further with dansyl chloride and therefore has nosignificant absorption in the dansyl signature region. Increasing thePEG length used in forming SiNS-8, SiNS-9, SiNS-10 increases the numberof residual surface amines available (owing to increasing steric demandsof the surface bound PEG) to further react with small molecules such asdansyl chloride (hence increasing the absorbance in the signature dansylregion). This effect seems to be maximal for SiNS-9 which is similar toSiNS-10.

FIG. 12C is a TEM of dansyl tagged PEGylated silica nanoshells SiNS-9(sample drop casted from aqueous solution before drying under ambientconditions).

FIG. 12D is a photograph of three vials containing (from left to right)SINS-2 (suspension in water), SiNS-8 (solution in water), and water(provided for reference).

FIG. 12E is a photograph of a vial containing SiNS-8 as a lyophilizedpowder.

FIGS. 13A and 13B are TEMs of dansylated silica nanoshells SINS-11(average diameter 30 nm) and SINS-12 (average diameter 20 nm),respectively. In this instance, a larger particle diameter indicatesincreased shell thickness.

FIG. 13C is a graph of the absorbance curves of dansylated silicananoshells SINS-11 and SiNS-12 after dialysis against tetrahydrofuranfor 72 hours, demonstrating the controlled release rate of the occludeddye within the silica nanoshells varies with shell thickness. A shellthickness of 30 nm (SiNS-11) released almost no porphyrin dye (retentionof peak at 420 nm), whereas the 20 nm shell thickness (SiNS-12) releasedsubstantially all of the porphyrin dye (loss of peak at 420 nm).

FIG. 14A is a TEM of iron oxide nanoshells SPIONNS-1.

FIG. 14B is a pair of photographs of vials, the left vial containing anaqueous solution of SPIONNS-1 having a rust orange hue, and the rightvial containing a brown colored lyophilized powder of SPIONNS-1.

FIG. 14C is a graph of the UV-VIS absorbance (left) and emission fromexcitation at 420 nm (right) of an aqueous solution of SPIONNS-1.

DETAILED DESCRIPTION

Disclosed are nano-sized shelled particles referred to herein asnanoshells, based on the discovery that inorganic materials, includingtetravalent silicon materials and/or metals, including zerovalent metal,metal oxides and other metal compounds, can be deposited in the form ofshell on the peripheral surface of a star polymer and/or a star polymerocclusion complex. A star polymer occlusion complex is an independentmacromolecule comprising a star polymer and a cargo material occludedtherein (e.g., biologically active materials, dyes, image enhancingagents). The cargo and/or the shell can be bound non-covalently and/orcovalently to the star polymer. The nanoshell can comprise a shellencompassing one or more star polymer macromolecules and/or one or moremacromolecules of a star polymer occlusion complex. The shell cancomprise any suitable inorganic material, organometallic material,and/or metal material. More particularly, the shell can comprise gold(e.g., as a metal and/or a salt), tetravalent silicon-containingmaterials (e.g., organosilicon materials, silicates, silica),iron-containing materials (e.g., as a metal, iron complexes, and/or ironoxides), which partially or wholly encapsulate the star polymer and/orstar polymer occlusion complex. That is, the shell can be contiguous ornon-contiguous, porous or non-porous. The nanoshells can comprise one ormore shell layers comprising the same or different inorganic materials.The nanoshells are useful, for example, as carriers for gene and drugdelivery, materials that can influence stem cell differentiation, and inparticular as carriers for materials useful in diagnostics or cellularimaging, such as contrast enhancing agents.

FIG. 1A is a three-dimensional drawing representation of a unimolecularstar polymer 10. FIG. 1B is a graphical layer diagram illustrating thehydrophilic and hydrophobic sub-regions of star polymer 10. Star polymer10 comprises six or more independent amphiphilic polymer arms 14. Eachpolymer arm 14 is covalently linked to a central crosslinked polymercore 16. Polymer core 16 can be a living core or a passive core (i.e.,having no reactive groups to introduce additional functionality).Polymer core 16 can be either hydrophobic or hydrophilic. In thisexample, each polymer arm 14 comprises a peripheral hydrophilic chainsegment 18 (dark tone in FIG. 1A) and an inner hydrophobic chain segment20 (white tone in FIG. 1A). Region 12 comprises the collection ofpolymer arms 14. In this example, region 12 has two sub-regions: aperipheral hydrophilic sub-region 22 (FIG. 1B) comprising the peripheralhydrophilic chain segments 18 and peripheral interstitial areas 24 (FIG.1A), and an inner hydrophobic sub-region 26 (FIG. 1B) composed of theinner hydrophobic chain segments 20 and inner interstitial areas 25(FIG. 1A). The dashed boundary lines around peripheral sub-region 22 andinner sub-region 26 in FIG. 1B indicate the boundary between peripheralinterstitial areas 24 and inner interstitial areas 25.

FIGS. 1A and 1B depict one example of an architecture for generatingwater compatible nanoshells. The hydrophilic and hydrophobicsub-regions, chain segments, and interstitial spaces can be reversed ifdesired. No restriction is placed on the number of the hydrophilicregions or the number of hydrophobic regions in the polymer arms (e.g.,hydrophilic blocks and hydrophobic blocks of a block copolymer arm). Thestar polymer can comprise one or more hydrophilic regions and/or one ormore hydrophobic regions, if desired. No restriction is placed on thearrangement of the hydrophilic regions or the number of hydrophobicregions. The peripheral region of the star polymer arm can behydrophobic or hydrophilic. The inner most region of the polymer armadjacent to the crosslinked star polymer core can be hydrophilic orhydrophobic. The peripheral sub-region 22, the inner sub-region 26,and/or the crosslinked polymer core 16 can also contain specific sitesfor further functionalization, which can be useful in controllingchemical interactions that favor the binding of, or the release of, anoccluded cargo material. As a non-limiting example, the polymer core 16can be a living core capable of initiating a polymerization orundergoing a different chemical modification. As another non-limitingexample, the polymer arms 14 can comprise a functionally useful endgroup 28, such as a galactose moiety capable of selective recognition ofliver cells.

The amphiphilic arms and the polymer core can be formed bypolymerization of a vinyl monomer, or by ring opening polymerization ofa cyclic carbonyl monomer.

FIG. 1C is a three-dimensional drawing representation of an exemplarystar polymer occlusion complex 30, comprising three occluded particles32 occluded in star polymer 10. Each occluded particle 32 can compriseone or more molecules of an occluded material. In the example shown, theoccluded material is in contact with the inner hydrophobic chainsegments 20 of star polymer 10 but may also reside to some extent incontact with the outer hydrophillic segments 18. In an embodiment, theoccluded material is a porphyrinoid, and the porphyrinoid is not in anaggregated state.

The shell can be in the form of a contiguous or non-contiguous layer.The shell can be porous or non-porous. The shell can compriseindependent nanoparticles of a material dispersed in the peripheralinterstitial areas 24 of a star polymer molecule. A shell can encompassone or more macromolecules of star polymer and/or star polymer occlusioncomplex. The general term “shell” includes any of these types ofdeposited inorganic layers, or a combination thereof, which are furtherillustrated in FIGS. 1D to 1G.

FIG. 1D is a three-dimensional drawing representation of an exemplarynanoshell 40 comprising a contiguous shell 46 disposed on a unimolecularstar polymer occlusion complex. The shell is partially removed to showthe star polymer occlusion complex 30 comprising occluded cargo material32 (e.g., a molecule of a dye).

FIG. 1E is a three-dimensional drawing representation of an exemplarynanoshell 50 comprising a shell 52 having pores 56. The star polymerocclusion complex 30 comprising occluded cargo material 32 is partiallyvisible within pores 56.

FIG. 1F is a three-dimensional drawing representation of an exemplarynanoshell 60 comprising independent nanoparticles 62 dispersed in theperipheral interstitial space 24 of the star polymer occlusion complex30. Inorganic particles 62 are in contact with peripheral hydrophilicchain segments 18 of polymer arms 14 (see FIG. 1A). Occluded cargomaterial 32 is associated with inner hydrophobic chain segments 20and/or core 16.

FIG. 1G is a three-dimensional drawing representation of an exemplarynanoshell 70, comprising shell 76 encompassing multiple independentmacromolecules of star polymer occluded complex 30. In this example, theshell is partially removed to reveal four macromolecules of the starpolymer occluded complex 30 contained therein.

The above examples of shells are meant to be illustrative andnon-limiting. The hydrophilic chain segments comprise functionality forcovalently or non-covalently binding the shell material. The shellmaterial can reside partially or wholly in the peripheral interstitialareas 24. Alternatively, the shell material can be covalently ornon-covalently bound, by one or more of the hydrophilic chain segments,as depicted in FIG. 1D.

Herein, “restricted metals” include ionic and nonionic forms ofberyllium, magnesium, calcium, strontium, barium, radium, aluminum,gallium, indium, thallium, germanium, tin, lead, arsenic, antimony,bismuth, tellurium, polonium, and metals of Groups 3 to 12 of thePeriodic Table. Metals of Groups 3 to 12 of the Periodic Table includescandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel,copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium,ruthenium, rhodium, palladium, silver, cadmium, lanthanum, cerium,praseodymium, neodymium, promethium, samarium, europium, gadolinium,terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium,hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold,mercury, actinium, thorium, protactinium, uranium, neptunium, plutonium,americium, curium, berkelium, californium, einsteinium, fermium,mendelevium, nobelium, lawrencium, rutherfordium, dubnium, seaborgium,bohrium, hassium, meitnerium, darmstadtium, roentgenium, andcopernicium. In an embodiment, the chemical formula of a star polymerused to prepare a star polymer occlusion complex contains none of theabove restricted metals. In another embodiment, each one of the aboverestricted metals has a concentration in a star polymer used to preparea star polymer occlusion complex of 0 parts per million to 100 parts permillion (ppm), 0 parts per billion to 100 parts per billion (ppb), or 0parts per trillion to 100 parts per trillion (ppt). Preferably, each oneof the above restricted metals has a concentration in a star polymerused to prepare a star polymer occlusion complex that is below detectionlimits. No restriction is placed on the concentration of boron, silicon,or any individual alkali metal in the chemical formula of a star polymerused to prepare a star polymer occlusion complex, as long as the starpolymer and the star polymer occlusion complex have desirableproperties, such as amphiphilic properties. The cargo material and/or aninorganic material used in forming a shell can comprise a restrictedmetal.

The cargo material can be bound covalently or non-covalently to the starpolymer. Non-covalent interactions include hydrophobic and/or ionicinteractions. The cargo material does not have to be released from thestar polymer occlusion complex in order to perform a useful function.The cargo material can perform a useful function while bound to the starpolymer or after release from the star polymer.

Preferably, the star polymer occlusion complex can be dispersed inaqueous solution in the form of nano-sized particles. Cargo materialsinclude biologically active substances. Exemplary biologically activesubstances include biomolecules (e.g., DNA, genes, peptides, proteins,enzymes, lipids, phospholipids, and nucleotides), natural or syntheticorganic compounds (e.g., drugs, dyes, synthetic polymers, oligomers, andamino acids), inorganic materials (e.g., metals and metal oxides),chromophores that aid in diagnostics (e.g., porphyrinoid compounds,including porphyrins and phthalocyanines), radioactive variants of theforegoing, and combinations of the foregoing. Some of the biologicallyactive substances can alter the chemical structure and/or activity of acell, or can selectively alter the chemical structure and/or activity ofa cell type relative to another cell type. As an example, one desirablechange in a chemical structure can be the incorporation of a gene intothe DNA of the cell. A desirable change in activity can be theexpression of a transfected gene. Another change in cell activity can bethe induced production of a desired hormone or enzyme. A desirablechange in cell activity can also be the selective death of one cell typeover another cell type. No limitation is placed on the relative changein cellular activity caused by the biologically active substance,providing the change is desirable and useful. Other biologically activematerials herein improve diagnostic capability without necessarilyaltering the structure or activity of the tissue, organ, bone, or cell.These include image contrast enhancing agents for magnetic resonanceimaging and x-ray imaging. The cargo material can comprise a metal,including one or more of the above-described restricted metals.

The term “biodegradable” is defined by the American Society for Testingand Materials as a degradation caused by biological activity, especiallyby enzymatic action, leading to a significant change in the chemicalstructure of the material. For purposes herein, a material isbiodegradable if it undergoes 60% biodegradation within 180 days inaccordance with ASTM D6400.

The star polymers used to prepare star polymer occlusion complexs areamphiphilic materials. Herein, an amphiphilic material is a materialthat can be dispersed in an aqueous mixture in the form of nano-sizedparticles having a circular cross-sectional diameter of 2 nm to 1500 nm.The star polymers are represented by the general formula (1):

wherein the wavy line represents the crosslinked polymer core (i.e.,core), and each T′ is an independent polymer arm covalently linked tothe core. The star polymer comprises w′ polymer arms T′, wherein w′ isgreater than or equal to 6. The star polymer has a particle size ofabout 2 nm to about 150 nm. Each of the 6 or more polymer arms comprisesa hydrophilic polymer chain segment and a hydrophobic polymer chainsegment. The polymer arms can independently comprise an optional sidechain polymer (i.e., a polymer pendant to the backbone of the polymerarm, also referred to herein as the second polymer). The polymer armscan independently also comprise a side chain functional group selectedfrom the group consisting of urea groups, carboxylic ester groups,carboxylic acid groups, carboxylic acid salts, latent carboxylic acidgroups, quaternary amine groups, tertiary amine groups, secondary aminegroups, primary amine groups, azides, alkynes, poly(alkylene ether)groups, and combinations thereof. The 6 or more polymer arms canindependently be living polymer arms, and the core can independently bea living core. The polymer arms and the core can independently comprisea homopolymer, random copolymer, block copolymer, or combinationsthereof.

The polymer arm can comprise a polymer chain segment comprising anitrogen-containing backbone. Exemplary nitrogen-containing backbonesinclude poly(alkylene imine)s having the formula—(—(CH₂—CH₂)_(m)—N(R)—)_(n), wherein R is alkyl or another substituent(e.g., a substituent comprising a carbonyl group attached to thebackbone nitrogen, and the like). The number average molecular weight ofthe polyamine chain segment can be from 100 to 100,000, morespecifically 100 to 10000, and even more specifically, 100 to 5000.

Star polymers as defined above preferably have a peripheral regioncontaining sites for interaction with inorganic materials. Thesestructures provide suitable scaffolds for the formation of inorganicnanoshells. If desired, the star polymer core and inner regions of thepolymer arms can provide sites for interaction with inorganic materials.In addition to this, the star polymer can be biodegradable or partiallybiodegradable. The ROP star polymers described further below providespecific but non-limiting examples of this.

Star Polymers Prepared by Vinyl Polymerizations.

Vinyl polymerization methods are well known and include but are notlimited to free radical polymerizations, living anionic additionpolymerizations, and living free radical polymerizations (e.g.,nitroxide mediated radical polymerization (NMP), atom radical transferPolymerization (ATRP), and reversible addition-fragmentation chaintransfer (RAFT)).

Exemplary vinyl monomers include styrene and substituted styrenes,divinylbenzene and substituted divinylbenzenes, (meth)acrylate esters,ethylene glycol di(meth)acrylates, (meth)acrylamides, acrylonitrile,vinyl acetate, vinyl chloride, ethene, propene, and butadiene. Othervinyl monomers will be readily apparent to those skilled in the polymerart.

ATRP polymerizations are typically initiated by an alkyl halide andcatalyzed by a transition metal. The reaction is illustrated in Scheme 1with the polymerization of styrene using copper(I) bromide as thecatalyst, ethyl 2-bromo-2-methylpropionate as the initiator, andN,N,N′,N,N pentamethyldiethylenetriamine (PMDETA) as a stabilizingligand.

ATRP produces polymers having narrow molecular distributions, but themetal catalyst can be cytotoxic and difficult to remove. Common monomersfor ATRP include (meth)acrylates, (meth)acrylamides, acrylonitrile, andstyrenes.

Anionic addition polymerizations of vinyl monomers (e.g., styrene,propene, butadiene), are typically initiated by nucleophilicalkyllithium compounds, Grignard reagents, metal alkoxides and metalhydroxides. The resulting anionic living polymers generally have lowpolydispersities but are non-biodegradable.

Star Polymers Prepared by Ring Opening Polymerization.

In an embodiment, the star polymers are biodegradable. Preferably, thesestar polymers have a polydispersity index of 1.35 or less. Thebiodegradable star polymers are preferably formed using a polymerizationmethod that involves the use of an organocatalyst rather than a catalystwhose chemical formula comprises a restricted metal. In an embodiment,the core of the star polymer includes 6 or more sites capable of furthersynthetic transformation, the sites including a functional groupselected from the group consisting of alcohols, amines, carboxylicacids, azides, alkynes, alkenes, halogen groups, and combinationsthereof.

The biodegradable star polymers are preferably derived by ring openingpolymerization of one or more cyclic carbonyl monomers usingorganocatalysis to form the polymer arms and the core. The chemicalformula of an organocatalyst comprises none of the above describedrestricted metals, including ionic and non-ionic forms of the restrictedmetal. The star polymers produced using an organocatalyst by ROP methodspreferably contain no more than 100 ppm of any single restricted metal.

Star polymers formed by organocatalyzed ring opening polymerizations ofcyclic carbonyl monomers have been found to have narrower molecularweight distributions (i.e., lower polydispersity indexes) compared tostar polymers formed by ring opening polymerization with a metal basedpolymerization catalyst. The molecular weight distributions are alsonarrower than star polymers prepared by free radical polymerizations(FRP). The star polymers formed by ring opening polymerization arebiodegradable, and they can be more biocompatible materials (i.e.,non-immunogenic, non-cytotoxic material) due to lower levels of metalcontaminants arising from a polymerization catalyst. In addition,sequential ROP polymerizations can be conducted in some instances in asingle vessel.

In one process of forming a star polymer, the polymer arms are preparedfirst, followed by the core, wherein the formation of the crosslinkedcore conjoins six or more amphiphilic polymer arms. In an embodiment, apolymer arm T′ has the general formula (2):

wherein the asterisk on the left of X^(a) indicates the attachmentpoint, or bond, to the core. Each P′ is a monovalent radicalrepresenting a peripheral hydrophilic polymer chain segment of thepolymer arm, and is derived from a first polymer. The first polymer canbe prepared by ring opening polymerization or by another type ofpolymerization. P′ can further comprise a substituent group selectedfrom the group consisting of urea groups, carboxylic acid groups,carboxylic acid salts, latent carboxylic acid groups, quaternary aminegroups, tertiary amine groups, secondary amine groups, primary aminegroups, azides, alkynes, poly(alkylene ether) groups, and combinationsthereof. In formula (2), the moiety

is a divalent radical comprising the hydrophobic chain segment of thepolymer arm, and is derived by ring opening polymerization of one ormore cyclic carbonyl monomers. The starred bond on the right side of thecarbonyl represents the attachment point to P′. Each X^(a) is a divalentradical independently selected from the group consisting of —O—, —NH—,

and —S—, wherein R⁴ is a monovalent radical comprising 1 to 30 carbons.K′ is a divalent radical comprising 1 to 10 backbone carbons linkingX^(a) to the carbonyl group. Each j is independently an integer greaterthan 1, more particularly greater than or equal to 4, and even moreparticularly greater than or equal to 10. Subscript j is chosen so as toachieve the desired hydrophobic/hydrophilic balance in the polymer arm,which depends on the backbone type of hydrophilic chain segment, theaverage molecular weight of the hydrophilic chain segment, and thecyclic carbonyl monomer or monomers used to prepare the hydrophobicchain segment. K′ can further comprise a functional side chain group F′.The hydrophobic chain segment comprises a backbone selected from thegroup consisting of polyesters, polycarbonates, polyureas,polycarbamates, polythiocarbamates, polydithiocarbamates, andcombinations thereof, which have a repeat structure as shown in (Table1):

TABLE 1 Polyester

Polycarbonate

Polyurea

Polycarbamate

Polythiocarbamate

Polythiocarbonate

Polydithiocarbonate

More particularly, a polymer arm has the general formula (3):

wherein X^(a), j, and P′ are defined as above. X^(b) and X^(c) are eachdivalent radicals independently selected from the group consisting of—O—,

—NH—, and —S—, wherein each R⁶ is independently hydrogen or a monovalenthydrocarbon radical comprising 1 to 30 carbons. Each R⁵ is independentlyhydrogen or a monovalent hydrocarbon radical comprising 1 to 30 carbons.Each m′ and n′ is independently zero or an integer from 1 to 5. Each o′is independently zero or an integer from 1 to 3. Each functional groupF′ is independently a monovalent radical comprising from 0 to 10000carbons. Subscripts m′, n′, and o′ together cannot be zero within thesame repeat unit. Each functional group F′ can independently comprise anon-polymeric group or a polymeric group, referred to herein as anoptional second polymer. The optional second polymer can be derived byring opening polymerization or another type of polymerization.

In one embodiment, each X′ and each X^(b) is oxygen, m′ and n′ are eachindependently an integer from 1 to 3, and o′ is zero or 1. In anotherembodiment, X^(c) is oxygen, and F′ is methyl or ethyl. In anotherembodiment, F′ comprises a second polymer. In still another embodiment,the second polymer comprises a polyether chain. In another embodiment,P′ comprises a polymer backbone selected from the group consisting ofpolyester, polycarbonate, and combinations thereof.

Scheme 2 illustrates the preparation of a biodegradable amphiphilic starpolymer by ring opening polymerization, wherein a Polymer Arm Precursoris prepared first, followed by the Polymer Core.

In this example mono methyl end capped poly(ethylene glycol) (FirstPolymer, MPEG) initiates polymerization of trimethylene carbonate (TMC)in the presence of a suitable organocatalyst, thereby producing thePolymer Arm Precursor. In this instance, the Polymer Arm Precursor is aliving block copolymer comprising a hydrophobic polycarbonate backbonesegment derived from TMC. This segment has a terminal hydroxyl groupcapable of initiating a ring opening polymerization. The ring openingpolymerization of BOD initiated by the Polymer Arm Precursor producesthe Polymer Core, conjoining six or more of the Polymer Arm Precursors,thereby forming the Star Polymer. In this instance, the Polymer Core isa highly crosslinked living network comprising a polyester repeatstructure, and further comprising six or more sites (terminal hydroxygroups) for further functionalization or ring opening polymerization ifdesired. The subscripts y and z indicate the relative moles of monomerused to make the Star Polymer. The subscript k is an integer greaterthan or equal to 6 and represents the number of Polymer Arms in the StarPolymer.

Thus, a method (Method 1) of preparing a polymer arm precursor comprisesagitating a mixture comprising a first polymer, a first cyclic carbonylmonomer, an organocatalyst comprising no structural metal, an optionalaccelerator, and an optional solvent, thereby forming the polymer armprecursor by ring opening polymerization of the cyclic carbonyl monomer.The polymer arm precursor is a living polymer and comprises ahydrophilic chain segment, a hydrophobic chain segment, and an initiatorgroup for ring opening polymerization. Herein, the polymer arm precursoris also referred to as a polymeric initiator for ring openingpolymerization of a core precursor material.

In a method (Method 2) of forming a star polymer, which can involve oneor more of the above-described polymerization techniques, a mixturecomprises: i) a polymer arm precursor comprising an initiator group forpolymerization, the arm precursor also comprising a hydrophobic polymerchain segment and a hydrophilic polymer chain segment, ii) a coreprecursor material comprising two or more polymerizable groups, iii) anorganocatalyst, iv) an optional accelerator, and v) an optional solvent.The mixture is agitated, thereby forming an amphiphilic star polymer bypolymerization of the core precursor material; wherein the star polymercomprises a crosslinked living polymer core derived from the coreprecursor material, the star polymer comprises 6 or more independentpolymer arms covalently linked to the core, the 6 or more polymer armsbeing derived from the polymer arm precursor, and the star polymercontains no more than 100 ppm of any single restricted metal. In anembodiment, the core precursor material comprises two or morepolymerizable cyclic carbonyl groups, and the polymer core is formed byring opening polymerization of the two or more cyclic carbonyl groups.In an embodiment, each of the 6 or more polymer arms comprises aperipheral hydrophilic chain segment, and a hydrophobic chain segmentlocated nearest the polymer core. In another embodiment, each of the 6or more polymer arms comprises a peripheral hydrophobic chain segment,and a hydrophilic chain segment located nearest the polymer core. Inanother embodiment, the polymeric initiator comprises a backbone segmentderived by ring opening polymerization of one or more cyclic carbonylmonomers. In another embodiment, the polymeric initiator comprises abackbone segment comprising a poly(alkylene oxide). In anotherembodiment, the organocatalyst comprises a nitrogen base comprisingthree or more nitrogens.

As shown above in Scheme 1, the polymer arm precursor is a free polymerchain as opposed to the 6 or more polymer arms of the star polymer,which are covalently linked to the polymer core. Initiation of ringopening polymerization of the core precursor material by the polymer armprecursors causes the polymer arm precursors to be conjoined by thegrowing crosslinked polymer core network. The core precursor materialand the cyclic carbonyl monomer can each comprise a functional groupselected from the group consisting of cyclic esters, cyclic carbonates,cyclic ureas, cyclic carbamates, cyclic thiocarbonates, cyclicthioureas, cyclic dithiocarbonates, and combinations thereof. In anembodiment, the core precursor material and the cyclic carbonyl monomereach comprise a functional group selected from the group consisting ofcyclic esters, cyclic carbonates, and combinations thereof. In anotherembodiment, the first polymer is a mono end capped poly(alkyleneglycol). In another embodiment, the method is performed in a singlereaction vessel without isolating the polymer arm precursor.

In another method (Method 3) of preparing a biodegradable amphiphilicstar polymer, the polymer arms are completed after formation of thepolymer core. The method comprises agitating a first mixture comprisinga first polymer comprising a protected functional group and annon-protected initiator group, a core precursor material comprising twoor more polymerizable groups, an organocatalyst, an optionalaccelerator, and an optional solvent, thereby forming a protected firststar polymer by polymerization of the core precursor material. Theprotected star polymer comprises a crosslinked polymer core and 6 ormore independent first polymer arms comprising a protected functionalgroup. The protected functional group of each of the 6 or more firstpolymer arms is then deprotected, thereby forming a second star polymercomprising 6 or more independent second polymer arms. The deprotectedfunctional group of the 6 or more independent second polymer arms can bean initiator group suitable for extending the second polymer arms bypolymerization. Alternatively, the deprotected functional group can beconverted to an active leaving group useful in extending the secondpolymer arms, for example by a nucleophilic displacement reaction. Theresulting star polymer comprises 6 or more independent polymer armscovalently bound to the polymer core, the polymer arms comprising ahydrophobic polymer chain segment and a hydrophilic polymer chainsegment.

The protected functional group of the first polymer arms can be in theform of a protected alcohol, protected amine, or protected thiol group,which when deprotected forms an alcohol, amine, or thiol, respectively.The deprotected initiator group is preferably in the terminal subunit ofeach of the 6 or more deprotected second polymer arms.

In the above-described methods, the hydrophilic chain segment of apolymer arm can be located at a peripheral end of each of the 6 or morepolymer arms, as illustrated in FIG. 1A. Alternatively, the hydrophobicchain segment can be located at the peripheral end of each of the 6 ormore polymer arms. This is illustrated in the molecular models of FIG.2A and FIG. 2B, wherein star polymer 40 comprises a shell 42 composed ofsix or more independent amphiphilic polymer arms 44, each of which iscovalently linked to a central polymer core 46. A polymer arm comprisesa peripheral hydrophobic chain segment 48 and an inner hydrophilic chainsegment 50. Shell 42 has two regions, a hydrophobic outer shell region56 (FIG. 2B) comprising peripheral hydrophobic chain segments 48 andinterstitial region 54 (FIG. 2A), and a hydrophilic inner shell region52 composed of the hydrophlic inner chain segments 50 and interstitialregion 54. The dashed boundary lines around inner shell region 52 andouter shell region 56 in FIG. 2B indicate the interstitial area isshared by the outer and inner shell regions. The polymer core 46 can beeither hydrophobic or hydrophilic. The outer shell region 56, the innershell region 52, and/or the polymer core 46 can further contain specificsites useful in controlling chemical interactions that favor the bindingof, or the release of, a biologically active cargo material. Forexample, the polymer core 46 can be a living core, capable of initiatinga polymerization or undergoing a different chemical modification. Asanother non-limiting example, the polymer arms 44 can comprise afunctionally useful end group 58, such as a galactose moiety capable ofselective recognition of liver cells.

A more specific method (Method 4) of preparing a polymer arm precursorcomprises agitating a reaction mixture comprising one or morehydrophobic cyclic carbonyl monomers, a hydrophilic first polymercomprising a ROP initiator group, an organocatalyst comprising nostructural metal, an optional accelerator, and an optional solvent,thereby forming a polymer arm precursor by ring opening polymerization.The polymer arm precursor is a living polymer, comprising an initiatorgroup for ring opening polymerization. The polymer arm precursorcomprises a hydrophobic chain segment derived from the one or morehydrophobic cyclic carbonyl monomers, and a hydrophilic chain segmentderived from the first polymer. In an embodiment, the first polymer is amono-end capped poly(alkylene glycol). In another embodiment, the firstpolymer is a poly(alkylene ether) comprising a protected amine end groupand a non-protected hydroxyl end group. The hydroxyl end group is aninitiator group for ring opening polymerization. In another embodiment,the first polymer comprises a mono end capped poly(ethylene glycol) or amono end capped polypropylene glycol).

The polymer arm precursor can be chemically modified to introduceadditional functionality after the ring opening polymerization. Forexample, the reaction mixture can comprise one or more latenthydrophobic cyclic carbonyl monomers, that is, a cyclic carbonyl monomerfrom which a hydrophobic repeat unit can be derived by a chemicaltransformation after the ring opening polymerization. Similarly, alatent hydrophilic cyclic carbonyl monomer is one from which ahydrophilic repeat unit can be derived by a chemical transformationafter the ring opening polymerization.

In another method (Method 5) of preparing a polymer arm precursor, thehydrophilic and hydrophobic chain segments of the polymer arm precursorare each derived by a ring opening polymerization. The method comprisesagitating a first mixture comprising one or more hydrophilic cycliccarbonyl monomers, an organocatalyst comprising no structural metal, anoptional accelerator, and an initiator, thereby forming a first polymerby ring opening polymerization, wherein the first polymer comprises aninitiator group for ring opening polymerization. A second mixture isformed comprising the first polymer, one or more hydrophobic cycliccarbonyl monomers, an optional second organocatalyst comprising nostructural metal, an optional second accelerator, and an optional secondsolvent. The mixture is agitated, thereby forming a polymer armprecursor, wherein the polymer arm precursor comprises a hydrophobicchain segment derived from the one or more hydrophobic cyclic carbonylmonomers, and a hydrophilic chain segment derived from the firstpolymer. The first mixture can include one or more latent hydrophiliccyclic carbonyl monomers, and the second mixture can include one or morelatent hydrophobic cyclic carbonyl monomers. The polymerizations can beperformed in reverse order.

When the hydrophilic chain segment and the hydrophobic chain segment areeach formed by a ring opening polymerization, the hydrophilic chainsegment and the hydrophobic chain segment can comprise repeat unitsderived from the same or different cyclic carbonyl monomers. Thehydrophilic chain segment and the hydrophobic chain segment canindependently comprise a backbone segment selected from the groupconsisting of polycarbonates, polyesters, polyureas, polycarbamates,polythiocarbamates, polythiocarbonates, polydithiocarbonates, andcombinations thereof.

The side chain groups and/or the end unit of the polymer arm or thepolymer arm precursor can be further chemically functionalized afterformation in order to control, for example, hydrophilic/hydrophobicbalance, water dispersibility, cell membrane recognition properties,binding properties with respect to a given cargo material, and/orrelease properties for a given cargo material.

The polymer arm, the polymer arm precursor, and the optional secondpolymer can independently comprise an optional end cap group (ECG). Endcap groups can impart stability and useful functionality to the finalstructure. End capping agents are numerous, and methods of their use arewell established in the polymer art. End capping agents can be selectedbased on the functionality desired and their intended use. In anembodiment, the optional end cap group comprises a moiety selected fromthe group consisting of alkyl ester groups, aryl ester groups,poly(alkylene ether) groups (e.g., poly(alkylene oxide)), thiol groups,amine groups, carboxylic acid groups, quaternary amine groups,functional groups capable of targeting specific cell types, andcombinations thereof. In an embodiment, the polymer arm comprises aperipheral end group comprising a galactose moiety for targeting livercells. In another embodiment, the peripheral end group comprises amannose moiety for binding mannose-specific proteins. In anotherembodiment, the peripheral end group comprises a quaternary amine.

The core precursor material for the ring opening polymerization can be amonomer, oligomer or a polymer comprising two or more polymerizablecyclic carbonyl moieties. More specifically, the core precursor materialcomprises two or more functional groups selected from the groupconsisting of cyclic esters, cyclic carbonates, cyclic carbamates,cyclic ureas, cyclic thiocarbamates, cyclic dithiocarbonates, andcombinations thereof. Non-limiting examples of core precursor materialsinclude bis-cyclic esters, bis-cyclic carbonates, bis-cyclic carbamates,bis-cyclic ureas, bis-cyclic thiocarbamates, and bis-cyclicdithiocarbonates. Exemplary bis-cyclic esters include but are notlimited to:

For simplicity, all examples herein assume the ideal case that allinitiating groups react and, therefore, the length of polymeric blocksmay be described by the division of the number of moles of monomer units(e.g., x, y, z, etc.) by the number of moles of initiating sites.However, the reaction of 100% of the initiating sites is not arequirement for successful implementation of the invention. Non-reactednucleophilic initiating groups can serve as additional reaction orinitiator sites during subsequent synthetic processes. Therefore, it isadvantageous that a high percentage of the nucleophilic initiatinggroups undergo the ring opening reaction.

The above reaction illustrated in Scheme 2 is not meant to berestrictive. For example, the reaction of TMC can be followed by asequential ring opening polymerization of a different hydrophobic cycliccarbonyl monomer, thereby forming a hydrophobic chain comprising a blockcopolymer derived from one or more hydrophobic cyclic carbonyl monomers.As stated above, the end cap group of the first polymer and/or thehydrophilic chain segment is optional. In addition, the hydrophilicchain segment or the hydrophobic chain segment can comprise a functionalgroup selected from the group consisting of urea groups, carboxylic acidgroups, carboxylic acid salts, latent carboxylic acid groups, quaternaryamine groups, tertiary amine groups, secondary amine groups, primaryamine groups, azides, alkynes, poly(alkylene ether) groups, andcombinations thereof, with the proviso that the water dispersibility andcarrier properties of the star polymer are not adversely affected.

Polyethers.

A polyether chain can provide an important means of introducinghydrophilicity into the star polymer. As stated above, a mono end cappedpolyether alcohol (e.g., poly(alkylene glycol) can be employed as aninitiator for ring opening polymerization of a cyclic carbonyl monomer,thereby introducing a main chain hydrophilic block into the resultingpolymer arm precursor.

The polyether alcohol can be a poly(alkylene glycol) of the generalformula (4):

HO—[C(R⁷)₂(C(R⁷)₂)_(a′)C(R⁷)₂O]_(n)—H  (4),

wherein a′ is 0 to 8, n is an integer from 2 to 10000, and each R⁷ isindependently a monovalent radical consisting of hydrogen and an alkylgroup of 1 to 30 carbons. Thus, the ether repeat unit comprises 2 to 10backbone carbons between each backbone oxygen. More particularly, thepoly(alkylene glycol) can be a mono endcapped poly(alkylene glycol),represented by the formula (5):

R⁸O—[C(R⁷)₂(C(R⁷)₂)_(a′)C(R⁷)₂O]_(n)—H  (5),

wherein R⁸ is a monovalent hydrocarbon radical comprising 1 to 20carbons.

As non-limiting examples, the polyether alcohol can be a poly(ethyleneglycol) (PEG), having the structure HO—[CH₂CH₂O]_(n)—H, wherein theether repeat unit CH₂CH₂O (shown in the brackets) comprises two backbonecarbons linked to a backbone oxygen. The polyether alcohol can also be apoly(propylene glycol) (PPG) having the structureHO—[CH₂CH(CH₃)O]_(n)—H, where the ether repeat unit CH₂CH(CH₃)Ocomprises two backbone carbons linked to a backbone oxygen with a methylside-chain. An example of mono end capped PEG is the commerciallyavailable monomethyl end capped PEG, wherein R⁸ is a methyl group. Otherexamples include poly(oxetane), having the structureHO—[CH₂CH₂CH₂O]_(n)—H, and poly(tetrahydrofuran), having the structureHO—[CH₂(CH₂)₂CH₂O]_(n)—H.

The mono end capped poly(alkylene glycol) can comprise more elaboratechemical structures, represented by the general formula (6):

Z′—[C(R⁷)₂(C(R⁷)₂)_(a′)C(R⁷)₂O]_(n-1)—H  (6),

wherein Z′ is a monovalent radical including the backbone carbons andoxygen of the end repeat unit, and can have 2 to 100 carbons. Thefollowing non-limiting examples illustrate mono end-derivatization ofpoly(ethylene glycol) (PEG). As described above, one end repeat unit ofPEG can be capped with a monovalent hydrocarbon group having 1 to 20carbons, such as the monomethyl PEG (MPEG), wherein Z′ is MeOCH₂CH₂O— asshown further above for MPEG in Scheme 2. The dash on the end of theMeOCH₂CH₂O— indicates the point of attachment to the polyether chain. Inanother example, Z′ includes a thiol group, such as HSCH₂CH₂O—, or athioether group, such as MeSCH₂CH₂O—. In another example, one end unitof PEG is an aldyhyde, wherein Z′ can be OCHCH₂CH₂O—. Treating thealdehyde with a primary amine produces an imine, wherein Z′ isR⁹N═CHCH₂CH₂O—. R⁹ is a monovalent radical selected from hydrogen, analkyl group of 1 to 30 carbons, or an aryl group comprising 6 to 100carbons. Continuing, the imine can be reduced to an amine, wherein Z′ isR⁹NHCH₂CH₂CH₂O—. In another example, one end repeat unit of PEG can beoxidized to a carboxylic acid, wherein Z′ is HOOCCH₂O—. Using knownmethods the carboxylic acid can be converted to an ester, wherein Z′becomes R⁹OOCCH₂O—. Alternatively, the carboxylic acid can be convertedto an amide, wherein Z′ becomes R⁹NHOCCH₂O—. Many other derivatives arepossible. In a particular embodiment, Z′ is a group comprising abiologically active moiety that interacts with a specific cell type. Forexample, the Z′ group can comprise a galactose moiety which specificallyrecognizes liver cells. In this instance, Z′ has the structure:

where L′ is a divalent linking group comprising 2 to 50 carbonscontaining the end repeat unit. The starred bond on the right side of L′indicates the attachment point to the polyether chain. Z′ can compriseother biologically active moieties such as mannose.

A polyether alcohol initiator for a ring opening polymerization cancomprise a poly(alkylene glycol) or a mono-derivatized poly(alkyleneglycol). The number average molecular weight of the polyether alcoholcan be from 100 to 100,000, more specifically 100 to 10000, and evenmore specifically, 100 to 5000.

Cyclic Carbonyl Monomers.

The cyclic carbonyl monomers can have the general formula (7):

wherein t is an integer from 0 to 6, and when t is 0, carbons labeled 4and 6 are linked together by a single bond. Each Y is a divalent radicalindependently selected from the group consisting of —O—, —S—,

wherein the dashes “—” indicate the point of attachment in the ring. Thelatter two groups are expressed herein as —N(Q¹)- and —C(Q¹)₂—. Each Q¹is an independent monovalent radical. Each Q¹ group can independently bebranched or non-branched. Each Q¹ group can independently comprise apolymer comprising from 1 to 10000 carbons. A Q¹ group can have thestructure

wherein the starred bond on the left side of the carbonyl indicates thepoint of attachment, M¹ is a monovalent radical, polymeric ornon-polymeric. As examples, each M¹ can independently be selected fromthe group consisting of —R¹, —OR¹, —NHR¹, —NR¹R¹, and —SR¹ wherein thedash represents the point of attachment, and each R¹ is an independentpolymeric or non-polymeric monovalent radical. In this example, each R¹can independently be selected from the group consisting of alkyl groupscomprising 1 to 100 carbons, and aryl groups comprising 6 to 100carbons. Each Q¹ group can independently comprise one or more additionalfunctional groups selected from the group consisting of ketone groups,aldehyde groups, alkene groups, alkyne groups, cycloaliphatic ringscomprising 3 to 10 carbons, heterocylic rings comprising 2 to 10carbons, ether groups, amide groups, ester groups, carboxylic acidgroups, urea groups, and combinations of the foregoing additionalfunctional groups. The heterocyclic ring can comprise oxygen, sulfurand/or nitrogen. Two or more Q¹ groups can together form a ring. In anembodiment, one or more of the Q¹ groups comprise a monovalent urearadical. In another embodiment, one or more of the Q¹ groups comprise alatent carboxylic acid group capable of being converted to a carboxylicacid after ring-opening polymerization. In another embodiment, one ormore of the Q¹ groups comprise a functional group capable of reactingwith a tertiary amine to form a quaternary amine. In another embodiment,each Q¹ is independently selected from the group consisting of hydrogen,alkyl groups comprising 1 to 100 carbons, and aryl groups comprising 6to 100 carbons. In another embodiment, at least one Q¹ group is a groupother than hydrogen.

A more specific cyclic carbonyl monomer has the general formula (8):

wherein each Q² and Q³ is an independent monovalent radical and R² is amonovalent radical, polymeric or non-polymeric. As examples, each Q² andQ³ can independently be selected from the group consisting of hydrogen,halides, alkyl groups having 1 to 100 carbons, and aryl groups having 6to 100 carbons. When Q² and Q³ are not hydrogen, Q² and Q³ representpendant moieties to the cyclic carbonyl ring that become side chains tothe ROP polymer chain. The —CO₂R² group also becomes a side chain to theROP polymer after ring opening polymerization. In an embodiment, each Q²is hydrogen and Q³ is a methyl or ethyl group. In another embodiment, R²comprises a monovalent urea radical. In another embodiment, R² comprisesa latent carboxylic acid group capable of being converted to acarboxylic acid after ring-opening polymerization. In anotherembodiment, R² comprises a functional group capable of reacting with atertiary amine to form a quaternary amine. In another embodiment, R²comprises a second polymer comprising from 1 to 10000 carbons.

Another more specific cyclic carbonyl monomer has the general formula(9):

wherein each Q⁴ is an independent monovalent radical, and u is aninteger from 1 to 8. As examples, each Q⁴ can independently be selectedfrom the group consisting of hydrogen, halides, alkyl groups comprising1 to 100 carbons, aryl groups comprising 6 to 100 carbon atoms, andgroups having the structure

wherein M¹ is a monovalent radical, polymeric or non-polymeric. Asexamples, M¹ can be selected from the group consisting of —R¹, —OR¹,—NHR¹, —NR¹R¹, and —SR¹ wherein the dash represents the point ofattachment, and R¹ is a monovalent radical, polymeric or non-polymeric.As examples, each R¹ can independently be selected from the groupconsisting of alkyl groups comprising 1 to 100 carbons, and aryl groupscomprising 6 to 100 carbons. When Q⁴ is not hydrogen, Q⁴ represents apendant moiety to the cyclic carbonyl ring that becomes a side chain tothe ROP polymer after ring opening polymerization. The lactone ring canoptionally comprise a carbon-carbon double bond; that is, optionally, a

group of formula (9) can independently represent a

group. The lactone ring can also comprise a heteroatom not linked to thering carbonyl or ring oxygen, such as oxygen, nitrogen, sulfur, or acombination thereof; that is, optionally a

group of formula (9) can independently represent a —O—, —S—, or —NR¹—group. In an embodiment, u is an integer from 1 to 6 and each Q⁴ ishydrogen. In an embodiment, one or more of the Q⁴ groups comprise amonovalent urea radical. In another embodiment, one or more of the Q⁴groups comprise a latent carboxylic acid group capable of beingconverted to a carboxylic acid after ring opening polymerization. Inanother embodiment, one or more of the Q⁴ groups comprise a functionalgroup capable of reacting with a tertiary amine to form a quaternaryamine.

The cyclic carbonyl monomer can have the general formula (10):

wherein each Q⁵ is an independent monovalent radical. As examples, eachQ⁵ can independently be selected from the group consisting of hydrogen,halides, alkyl groups comprising 1 to 100 carbons, aryl groupscomprising 6 to 100 carbon atoms, and groups having the structure

wherein M¹ is a monovalent radical, polymeric or non-polymeric, and eachv is independently an integer from 1 to 6. As examples, M¹ can beselected from the group consisting of —R¹, —OR¹, —NHR¹, —NR¹R¹, and —SR¹wherein the dash represents the point of attachment, and R¹ is amonovalent radical, polymeric or non-polymeric. As examples, each R¹ canindependently be selected from the group consisting of alkyl groupscomprising 1 to 100 carbons, and aryl groups comprising 6 to 100carbons. Each Q⁶ is an independent monovalent radical. As examples, eachQ⁶ can independently be selected from the group consisting of hydrogen,alkyl groups having 1 to 100 carbons, and aryl groups having 6 to 100carbons. When Q⁵ and Q⁶ are not hydrogen, Q⁵ and Q⁶ represent pendantmoieties to the cyclic carbonyl ring that become side chains to the ROPpolymer after ring opening polymerization. In an embodiment, each v is1, each Q⁵ is hydrogen, and each Q⁶ is a hydrocarbon group comprising 1to 6 carbons. In an embodiment, one or more of the Q⁵ and/or Q⁶ groupscomprise a monovalent urea radical. In another embodiment, one or moreof the Q⁵ and/or Q⁶ groups comprise a latent carboxylic acid groupcapable of being converted to a carboxylic acid after ring-openingpolymerization. In another embodiment, one or more of the Q⁵ and/or Q⁶groups comprise a functional group capable of reacting with a tertiaryamine to form a quaternary amine.

In an embodiment, the polymer arm comprises repeat units derived from acyclic carbonyl monomer of the general formula (11):

wherein each Y is independently selected from the group consisting of—O—, —NH—,

and —S—, R⁵ and R⁶ are independent monovalent radicals comprising 1 to30 carbons, and M¹ is selected from the group consisting of —OR¹, —NHR¹,—NR¹R¹, and —SR¹ wherein the dash represents the point of attachment,and R¹ is a monovalent radical. M¹ can comprise a non-polymeric group ora second polymer, wherein the second polymer comprises 1 to 10000carbons.

The cyclic carbonyl monomer can comprise a latent carboxylic acid.Non-limiting examples of latent carboxylic acids include esters that canbe hydrolyzed under mild conditions (e.g., trifluoroethyl ester,pentafluorophenyl ester, or p-nitrophenyl ester, N-hydroxysuccinimimideester, trimethylsilyl ester, tetrahydropyranyl ester). Other latentcarboxylic acids include thermally labile tertiary esters (e.g., t-butylesters). Still other latent carboxylic acids include esters capable ofbeing reductively cleaved using hydrogen and a suitable catalyst (e.g.,benzyl esters, cleavable by H₂/Pd—C). In an embodiment, the latentcarboxylic acid group is any carboxylic ester that can be converted to acarboxylic acid by hydrogenation using a suitable catalyst. One exampleis the benzyl ester of MTCOBn.

The benzyl ester of MTCOBn can be cleaved to a carboxylic acid usingH₂/Pd—C after the ring opening polymerization.

Another example of a latent carboxylic acid group is an acetal-protectedcarboxylic acid group, herein also referred to as an acetal ester group.The acetal ester group has the general formula (12):

wherein the starred bond (*) represents the site of attachment to acyclic carbonyl moiety, and R^(c) and R^(d) are monovalent radicalsindependently comprising from 1 to 20 carbons. In an embodiment, R^(c)is methyl and R^(d) is ethyl. An example of cyclic carbonyl compoundcomprising an acetal ester is MTCOEE:

When copolymerized into the polymer, repeat units derived from MTCOEEcomprise a side chain acetal ester that is readily deprotected in theacidic endosomal environment. Once released into the cytoplasm, theresulting carboxylic acid groups of the cationic polymer can bedeprotonated.

Additional cyclic carbonyl monomers of formulas (8), (9), and (10) arelisted in Table 2.

TABLE 2

The cyclic carbonyl monomers can be purified by recrystallization from asolvent such as ethyl acetate or by other known methods of purification,with particular attention being paid to removing as much water aspossible from the monomer. The monomer moisture content can be from 1 to10,000 ppm, 1 to 1,000 ppm, 1 to 500 ppm, and most specifically 1 to 100ppm, by weight of the monomer.

The cyclic carbonyl monomers can also comprise isotopically enrichedforms of the cyclic carbonyl monomers. These include functional groupscomprising elements selected from the group consisting of ¹³C, ¹⁴C, ¹⁵N,deuterium, tritium, and combinations thereof. The cyclic carbonylmonomers can also comprise a radioactive moiety suitable for targeting aspecific cell type, such as a cancer cell.

The cyclic carbonyl monomers can comprise a reactive monovalent leavinggroup that when treated with a tertiary amine, produces a quaternaryamine. Reactive monovalent leaving groups include alkyl halides (e.g.,alkyl chlorides, alkyl bromides, or alkyl iodides), sulfonate esters(e.g., tosylates, or mesylates), epoxides, and oxetanes. Reaction withthe tertiary amine is generally performed after the ring openingreaction when the reactive monovalent leaving group occupies a sidechain position in the ROP polymer.

The tertiary amine can comprise a single nitrogen such as atrialkylamine, including but not limited to trimethylamine,triethylamine, tripropylamine, and the like. The tertiary amine canfurther comprise additional functional groups, in particular acarboxylic acid group, for example 3-(N,N-dimethylamino)propionic acid.In such instances, the cationic polymer will comprise first repeat unitscomprising a side chain moiety comprising a quaternary amine and acarboxylic acid group.

The tertiary amine can also comprise isotopically enriched versions ofthe tertiary amine, such as trimethylamine-¹⁴C, trimethylamine-¹⁵N,trimethylamine-¹⁵N, trimethyl-¹³C₃-amine, trimethyl-d₉-amine, andtrimethyl-d₉-amine-¹⁵N. The tertiary amine can also comprise aradioactive moiety suitable for targeting a specific cell type, such asa cancer cell.

The tertiary amine can be a bis-tertiary amine of the general formula(13):

where L″ is a divalent linking group comprising 2 to 30 carbons, andeach monovalent Rb group is independently selected from alkyl groupscomprising 1 to 30 carbons or aryl groups comprising 6 to 30 carbons.Each R^(b) group can independently be branched or non-branched. EachR^(b) group can independently comprise additional functional groups suchas a ketone group, aldehyde group, hydroxyl group, alkene group, alkynegroup, cycloaliphatic ring comprising 3 to 10 carbons, heterocylic ringcomprising 2 to 10 carbons, ether group, amide group, ester group, andcombinations of the foregoing additional functional groups. Theheterocyclic ring can comprise oxygen, sulfur and/or nitrogen. Two ormore Rb groups can also together form a ring. Representative L″ groupsinclude —(CH₂)_(z′)— where z′ is an integer from 2 to 30,—(CH₂CH₂O)_(z″)CH₂CH₂— where z″ is an integer from 1 to 10,—CH₂CH₂SCH₂CH₂—, —CH₂CH₂SSCH₂CH₂—, —CH₂CH₂SOCH₂CH₂—, and—CH₂CH₂SO₂CH₂CH₂—. L″ can further comprise a monovalent or divalentcycloaliphatic ring comprising 3 to 20 carbons, a monovalent or divalentaromatic ring comprising 6 to 20 carbons, a ketone group, aldehydegroup, hydroxyl group, alkene group, alkyne group, a heterocylic ringcomprising 2 to 10 carbons, ether group, amide group, ester group, andcombinations of the foregoing functional groups. The heterocyclic ringcan comprise oxygen, sulfur and/or nitrogen. The bis-tertiary amine canalso comprise isotopically enriched forms of the bis-tertiary amine,such as deuterium, carbon-13, and/or nitrogen-15 enriched forms thereof.

More specific bis-tertiary amines includeN,N,N′,N′-tetramethyl-1,2-ethanediamine (TMEDA),N,N,N′,N′-tetramethyl-1,3-propanediamine (TMPDA),N,N,N′,N′-tetramethyl-1,4-butanediamine (TMBDA),N,N,N′,N′-tetraethyl-1,2-ethanediamine (TEEDA),N,N,N′,N′-tetraethyl-1,3propanediamine (TEPDA),1,4-bis(dimethylamino)cyclohexane, 1,4-bis(dimethylaminobenzene),N,N,N′,N′-tetraethyl-1,4-butanediamine (TEBDA), 4-dimethylaminopyridine(DMAP), 4,4-dipyridyl-1,4-diazabicyclo[2.2.2]octane (DABCO),4-pyrrolidinopyridine, 1-methylbenzimidazole, and combinations thereof.In an embodiment, the bis-tertiary amine is TMEDA.

The above-described cyclic carbonyl monomers undergo ring-openingpolymerization to form a ROP polymers in atactic, syndiotactic orisotactic forms. The particular tacticity depends on the cyclicmonomer(s), isomeric purity, and the reaction conditions.

The reaction mixture for the ring opening polymerization comprises oneor more cyclic carbonyl monomers; a catalyst; an optional accelerator;an optional solvent, and an initiator. The ring opening polymerizationis generally conducted in a reactor under inert atmosphere such asnitrogen or argon. The polymerization can be performed by solutionpolymerization in an anhydrous non-protic solvent such as benzene,toluene, xylene, cyclohexane, n-hexane, dioxane, chloroform anddichloroethane, or by bulk polymerization. The reaction temperature canbe from about ambient temperature to 250° C. Generally, the reactionmixture is heated at atmospheric pressure for 0.5 to 72 hours to effectpolymerization, forming a second mixture.

Less preferred catalysts for ring opening polymerizations include metaloxides such as tetramethoxy zirconium, tetra-iso-propoxy zirconium,tetra-iso-butoxy zirconium, tetra-n-butoxy zirconium, tetra-t-butoxyzirconium, triethoxy aluminum, tri-n-propoxy aluminum, tri-iso-propoxyaluminum, tri-n-butoxy aluminum, tri-iso-butoxy aluminum, tri-sec-butoxyaluminum, mono-sec-butoxy-di-iso-propoxy aluminum, ethyl acetoacetatealuminum diisopropylate, aluminum tris(ethyl acetoacetate), tetraethoxytitanium, tetra-iso-propoxy titanium, tetra-n-propoxy titanium,tetra-n-butoxy titanium, tetra-sec-butoxy titanium, tetra-t-butoxytitanium, tri-iso-propoxy gallium, tri-iso-propoxy antimony,tri-iso-butoxy antimony, trimethoxy boron, triethoxy boron,tri-iso-propoxy boron, tri-n-propoxy boron, tri-iso-butoxy boron,tri-n-butoxy boron, tri-sec-butoxy boron, tri-t-butoxy boron,tri-iso-propoxy gallium, tetramethoxy germanium, tetraethoxy germanium,tetra-iso-propoxy germanium, tetra-n-propoxy germanium, tetra-iso-butoxygermanium, tetra-n-butoxy germanium, tetra-sec-butoxy germanium andtetra-t-butoxy germanium; halogenated compound such as antimonypentachloride, zinc chloride, lithium bromide, tin(IV) chloride, cadmiumchloride and boron trifluoride diethyl ether; alkyl aluminum such astrimethyl aluminum, triethyl aluminum, diethyl aluminum chloride, ethylaluminum dichloride and tri-iso-butyl aluminum; alkyl zinc such asdimethyl zinc, diethyl zinc and diisopropyl zinc; heteropolyacids suchas phosphotungstic acid, phosphomolybdic acid, silicotungstic acid andalkali metal salt thereof; zirconium compounds such as zirconium acidchloride, zirconium octanoate, zirconium stearate and zirconium nitrate.

Metal from a polymerization catalyst can be entrapped by the crosslinkedpolymer core of the star polymer. The trapped metal can be cytotoxic andcan interfere with the binding, release and/or the function of a cargomaterial and/or inorganic shell. Therefore, star polymers comprising aminimum of each restricted metal described further above is highlydesirable.

Preferred catalysts for the ring opening polymerization areorganocatalysts. An organocatalyst overcomes the problem of entrappedmetal, in addition to providing a platform for synthesizing ring openedpolymers of controlled, predictable molecular weights and narrowpolydispersities. Examples of organocatalysts for ring openingpolymerization of cyclic esters, cyclic carbonates and siloxanes are4-dimethylaminopyridine, phosphines, N-heterocyclic carbenes (NHC),bifunctional aminothioureas, phosphazenes, amidines, and guanidines. Inan embodiment the catalyst isN-(3,5-trifluoromethyl)phenyl-N′-cyclohexyl-thiourea (TU):

Other organocatalysts comprise at least one1,1,1,3,3,3-hexafluoropropan-2-ol-2-yl (HFP) group. Singly-donatinghydrogen bond catalysts have the formula (14):

R²—C(CF₃)₂OH  (14).

R² represents a hydrogen or a monovalent radical having from 1 to 20carbons, for example an alkyl group, substituted alkyl group, cycloalkylgroup, substituted cycloalkyl group, heterocycloalkyl group, substitutedheterocycloalklyl group, aryl group, substituted aryl group, or acombination thereof. Exemplary singly-donating hydrogen bondingcatalysts are listed in Table 3.

TABLE 3

Doubly-donating hydrogen bonding catalysts have two HFP groups,represented by the general formula (15):

wherein R³ is a divalent radical bridging group containing from 1 to 20carbons, such as an alkylene group, a substituted alkylene group, acycloalkylene group, a substituted cycloalkylene group, aheterocycloalkylene group, substituted heterocycloalkylene group, anarylene group, a substituted arylene group, or a combination thereof.Representative double hydrogen bonding catalysts of formula (15) includethose listed in Table 4. In a specific embodiment, R² is an arylene orsubstituted arylene group, and the HFP groups occupy positions meta toeach other on the aromatic ring.

TABLE 4

In one embodiment, the catalyst is selected from the group consisting of4-HFA-St, 4-HFA-Tol, HFTB, NFTB, HPIP, 3,5-HFA-MA, 3,5-HFA-St, 1,3-HFAB,1,4-HFAB, and combinations thereof.

Also contemplated are organocatalysts comprising HFP-containing groupsbound to a support. In one embodiment, the support comprises a polymer,a crosslinked polymer bead, an inorganic particle, or a metallicparticle. HFP-containing polymers can be formed by known methodsincluding direct polymerization of an HFP-containing monomer (forexample, the methacrylate monomer 3,5-HFA-MA or the styryl monomer3,5-HFA-St). Functional groups in HFP-containing monomers that canundergo direct polymerization (or polymerization with a comonomer)include acrylate, methacrylate, alpha, alpha,alpha-trifluoromethacrylate, alpha-halomethacrylate, acrylamido,methacrylamido, norbornene, vinyl, vinyl ether, and other groups knownin the art. Alternatively, pre-formed polymers and other solid supportsurfaces can be modified by chemically bonding an HFP-containing groupto the polymer or support via a linking group. Examples of linkinggroups include C₁-C₁₂ alkyl, C₁-C₁₂ heteroalkyl, an ether group, athioether group, an amino group, an ester group, an amide group, or acombination thereof. Also contemplated are catalysts comprising chargedHFP-containing groups bound by ionic association to oppositely chargedsites on a polymer or a support surface.

The organocatalyst can also be a nitrogen base, as indicated above.Exemplary nitrogen base catalysts include triallylamine, triethylamine,tri-n-octylamine and benzyldimethylamine. Other nitrogen base catalysts,listed in Table 5, include pyridine (Py), N,N-dimethylaminocyclohexane(Me₂NCy), 4-N,N-dimethylaminopyridine (DMAP), trans1,2-bis(dimethylamino)cyclohexane (TMCHD),1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD),7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), (−)-sparteine, (Sp)1,3-bis(2-propyl)-4,5-dimethylimidazol-2-ylidene (Im-1),1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (Im-2),1,3-bis(2,6-di-1-propylphenyl(imidazol-2-ylidene (Im-3),1,3-bis(1-adamantyl)imidazol-2-ylidene (Im-4),1,3-di-1-propylimidazol-2-ylidene (Im-5),1,3-di-t-butylimidazol-2-ylidene (Im-6),1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene (Im-7),1,3-bis(2,6-di-1-propylphenyl)-4,5-dihydroimidazol-2-ylidene,1,3-bis(2,6-di-1-propylphenyl)-4,5-dihydroimidazol-2-ylidene (Im-8) or acombination thereof

TABLE 5

The above-described nitrogen bases can be used alone as a catalyst whenproducing linear polymers by ring opening polymerization, such as thepolymer arm precursor. Alternatively, the nitrogen bases can serve as anoptional accelerator when used in combination with a primary catalyst,such as TU, in a ring opening polymerization. When employed as anaccelerator, each nitrogen is potentially capable of participating as aLewis base. In general, stronger nitrogen base accelerators improve thepolymerization rate.

Exceptions to the above have been found when attempting to generate thepolymer core by ring opening polymerization using base catalysis alone.In these instances, nitrogen bases comprising 1 or 2 nitrogens were noteffective in forming unimolecular star polymers. The 1-nitrogen and2-nitrogen base catalysts produced star polymers having highpolydispersities (greater than 1.35), or products that were amorphous.Preferred nitrogen bases for the formation of the polymer core by ringopening polymerization of a bis-cyclic carbonyl monomer have three ormore nitrogens. Unimolecular nano-sized amphiphilic star polymers havinga polydispersity of 1.35 or less were successfully produced using thistype of catalyst. One such base catalyst is1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). In some instances the starpolymer can be formed using TBD as the sole catalyst. The star polymercan have a polydispersity index of 1.26, a hydrodynamic radius of 10.9nm, and contains less than 100 ppm of any restricted metal.

The ROP reaction mixture comprises at least one catalyst and, whenappropriate, several catalysts together. The ROP catalyst is added in aproportion of 1/20 to 1/40,000 moles relative to the cyclic carbonylmonomers, and preferably of 1/100 to 1/20,000 moles.

The ROP reaction mixture also comprises an initiator. Initiatorsgenerally include nucleophiles such as alcohols, amines and thiols. Theinitiator can be monofunctional, difunctional, or multifunctional. Theinitiator can be polymeric or non-polymeric. For example, the initiatorcan be a polymeric alcohol, polymeric amine, or polymeric thiol.

More particularly, the initiator for the ring opening reaction is analcohol. The alcohol initiator can be any suitable alcohol, includingmono-alcohol, diol, triol, or other polyol, with the proviso that thechoice of alcohol does not adversely affect the polymerization yield,polymer molecular weight, complexation with a biologically activematerial, and/or the desirable mechanical and physical properties of thestar polymer. The alcohol can be multi-functional comprising, inaddition to one or more hydroxyl groups, a halide, an ether group, anester group, an amide group, or other functional group. Exemplaryalcohols includes methanol, ethanol, propanol, butanol, pentanol, amylalcohol, capryl alcohol, nonyl alcohol, decyl alcohol, undecyl alcohol,lauryl alcohol, tridecyl alcohol, myristyl alcohol, pentadecyl alcohol,cetyl alcohol, heptadecyl alcohol, stearyl alcohol, nonadecyl alcoholand other aliphatic saturated alcohols, cyclopentanol, cyclohexanol,cycloheptanol, cyclooctanol and other aliphatic cyclic alcohols; phenol,substituted phenols, benzyl alcohol, substituted benzyl alcohol,benzenedimethanol, trimethylolpropane, a saccharide, poly(ethyleneglycol), propylene glycol, alcohol functionalized block copolymersderived from oligomeric alcohols, alcohol functionalized branchedpolymers derived from branched alcohols, or a combination thereof.Monomeric diol initiators include ethylene glycols, propylene glycols,hydroquinones, and resorcinols. An example of a diol initiator is BnMPA,derived from 2,2-dimethylol propionic acid.

BnMPA is a precursor used in the preparation of cyclic carbonatemonomers.

The ring-opening polymerization can be performed with or without the useof a solvent, more particularly with a solvent. Optional solventsinclude dichloromethane, chloroform, benzene, toluene, xylene,chlorobenzene, dichlorobenzene, benzotrifluoride, petroleum ether,acetonitrile, pentane, hexane, heptane, 2,2,4-trimethylpentane,cyclohexane, diethyl ether, t-butyl methyl ether, diisopropyl ether,dioxane, tetrahydrofuran, or a combination comprising one of theforegoing solvents. When a solvent is present, a suitable cycliccarbonyl monomer concentration is about 0.1 to 5 moles per liter, andmore particularly about 0.2 to 4 moles per liter.

The ring-opening polymerization can be performed at a temperature thatis about ambient temperature or higher, more specifically a temperaturefrom 15° C. to 200° C., and more particularly 20° C. to 200° C. When thereaction is conducted in bulk, the polymerization is performed at atemperature of 50° C. or higher, and more particularly 100° C. to 200°C. Reaction times vary with solvent, temperature, agitation rate,pressure, and equipment, but in general the polymerizations are completewithin 1 to 100 hours.

Whether performed in solution or in bulk, the ring openingpolymerizations are conducted in an inert (i.e., dry) atmosphere and ata pressure of from 100 to 500 MPa (1 to 5 atm), more typically at apressure of 100 to 200 MPa (1 to 2 atm). At the completion of thereaction, the solvent can be removed using reduced pressure.

The nitrogen base accelerator, when used, is present in an amount of 0.1to 5.0 mol %, 0.1 to 2.5 mol %, 0.1 to 1.0 mol %, or 0.2 to 0.5 mol %,based on total moles of cyclic carbonyl monomer.

The amount of initiator for the ring opening polymerization iscalculated based on the equivalent molecular weight per nucleophilicinitiating group in the initiator (e.g., alcohol groups). The initiatinggroups are preferably present in an amount of 0.001 to 10.0 mol %, 0.1to 2.5 mol %, 0.1 to 1.0 mol %, and 0.2 to 0.5 mol %, based on totalmoles of cyclic carbonyl monomer. For example, if the molecular weightof the initiator is 100 g/mole and the initiator has 2 hydroxyl groups,the equivalent molecular weight per hydroxyl group is 50 g/mole. If thepolymerization calls for 5 mol % hydroxyl groups per mole of monomer,the amount of initiator is 0.05×50=2.5 g per mole of monomer.

In a specific embodiment, the catalyst is present in an amount of about0.2 to 20 mol %, and the hydroxyl groups of the initiator are present inan amount of 0.1 to 5.0 mol % based on the equivalent molecular weightper nucleophilic group in the initiator.

As stated above, the ring opening polymerization forms a polymer chaincomprising a living polymer segment. In an embodiment, one backbonerepeating unit of the ROP polymer chain is an ester repeating unit. TheROP polymer backbone can, for example, also comprise a polyesterhomopolymer, a random polyester copolymer, a polycarbonate homopolymer,a random polycarbonate copolymer, or a random polyestercarbonatecopolymer. The ROP polymer chain can comprise a terminal hydroxyl group,terminal thiol group, or terminal amine group, each of which caninitiate further ROP chain growth, if desired.

The ROP polymer can comprise hydrophilic repeat units, hydrophobicrepeat units, and combinations thereof, thereby imparting amphiphilicproperties to the star polymer. The ROP polymer chains can have a numberaverage molecular weight M_(n) as determined by size exclusionchromatography of at least 2500 g/mol, more specifically 4000 g/mol to150000 g/mol, and even more specifically 10000 g/mol to 50000 g/mol. Inan embodiment, the ROP polymer chain has a number average molecularweight M_(n) of 10000 to 20000 g/mole. The ROP polymer chains also havea narrow polydispersity index (PDI), generally less than or equal to1.35, more particularly from 1.01 to 1.35, even more particularly 1.1 to1.30, and still more particularly 1.1 to 1.25.

As stated above, the ROP polymer can comprise a pendant latentcarboxylic acid group, such as a benzyl ester. In this instance, thelatent carboxylic acid group can be deprotected using H₂/Pd—C to form apendant carboxylic acid group. If the protected carboxylic acid is inthe form of a thermally labile carboxylic ester, such as a t-butylester, deprotection can be effected by heating the ROP polymer. If theprotected carboxylic acid is hydrolytically unstable, such as atrifluoroethyl ester, the ROP polymer can be deprotected with mildaqueous acid or base to form a pendant carboxylic acid group. In aparticular embodiment, the protected carboxylic acid is a benzyl ester.

The star polymers can comprise repeat units comprising a positivecharge, a negative charge, or a mixture thereof.

In aqueous solution the star polymers disperse to form nanoparticleshaving an average particle size of from about 2 nm to about 500 nm,about 10 nm to about 250 nm, and more particularly about 50 nm to about200 nm, about 50 nm to about 150 nm, about 50 nm to about 120 nm, andeven more particularly from about 50 nm to about 100 nm, as measured bydynamic light scattering. For the foregoing particle sizes, the aqueoussolution can have a pH of from 5.0 to 8.0. This pH range can beincreased for non-biodegradable compositions, such as those having apolymer core prepared from divinylbenzene.

Star Polymer Occlusion Complexes.

A star polymer occlusion complex comprises a star polymer and a suitablecargo material occluded therein. In an embodiment, the cargo material isselected from the group consisting of drugs, genes, dyes, image contrastenhancing materials, and combinations thereof. The cargo material cancomprise a metal, including one or more of the above-describedrestricted metals. The cargo material can also comprise a radioactivemetal. In aqueous solution at a pH of from 5.0 to 8.0, the star polymerocclusion complexes have an average particle size of from 2 nm to 500nm, 2 nm to 250 nm, 2 nm to 150 nm, 2 nm to 120 nm, and moreparticularly 10 nm to 120 nm, 20 nm to 120 nm, 30 nm to 120 nm, and evenmore particularly from 50 nm to 120 nm, as measured by dynamic lightscattering. The star polymer occlusion complexes can comprise, forexample 0.1 to 90 wt. %, more particularly 5 to 50 wt. %, and even moreparticularly 15 to 50 wt. % of a biologically active material based ontotal dry weight of the star polymer occlusion complexes. In anembodiment, the biologically active cargo material is a drug. In anotherembodiment, the biologically active material is a contrast enhancingagent.

The star polymer occlusion complexes can comprise both small molecularweight biologically active materials in the size range from 100 daltonsto about 1,000 daltons as well as larger macromolecular materials, suchas peptide and protein drugs in the size range from about 1,000 daltons(Da) to about 100,000 daltons, and beyond.

Contrast enhancing agents that have been considered for nuclear magneticresonance imaging include soluble salts of paramagnetic metal ions,paramagnetic chelates and metallic complexes, and nitroxide stable freeradicals. Paramagnetic metals ions include: from the transition metalsseries: titanium (Ti³⁺), iron (Fe³⁺), vanadium (V⁴⁺), cobalt (Co³⁺),chromium (Cr³⁺), nickel (Ni²⁺), manganese (Mn²⁺), and copper (Cu²⁺);from the Lanthanide series: praseodynium (Pr³⁺), gadolinium (Gd³⁺),europium (Eu³⁺), and dysprosium (Dy³⁺); from the Actinide series:protactinium (Pa⁴⁺); and from nitroxide stable free radicals:pyrrolidine derivatives, and piperidine derivatives. Of these, the mostfavored contrast enhancing agents include complexes of ferric, chromium,and gadolinium ions, and stable nitroxide free radicals. Exemplarycontrast enhancing agents for x-ray imaging include barium salts andhalogenated materials, more particularly brominated and/or iodinatedmaterials.

Organic contrast enhancing agents include porphyrinoids, which includebut are not limited to porphyrins, corrins, chlorins,bacteriochlorophylls, phthalocyanines, tetraazaphyrins, texaphyrins,saphyrins, and the like. A nonlimiting example of a porphyrinoidcompound is 5,10,15,20-(3,5-ditertbutylphenyl)porphyrin, where theligand M can be a metal or two hydrogens (M=2H) (DTBP):

Another non-limiting example of a porphyrinoid compound is tert-butylphthalocyanine, wherein the ligand M can be a metal or two hydrogens(M=2H) (TBP):

The contrast enhancing material can also comprise a combination of aporphyrinoid compounds. The porphyrinoid compound can further comprise ametal ligand that is a restricted metal.

The porphyrinoid compound can be in a non-aggregated state in the starpolymer occlusion complex, detectable by the fluorescence of an aqueousmixture of the star polymer occlusion complex. In an embodiment, 10% to100% by weight of the porphyrinoid compound in the star polymerocclusion complex is in a non-aggregated state. In another embodiment,50% to 100% by weight of the porphyrinoid compound in the star polymerocclusion complex is in a non-aggregated state.

Exemplary protein drugs include peptide hormones such as insulin,glucagon, parathyroid hormone, calcitonin, vasopression, renin,prolactin, growth hormone; the gonadotropins including chorionicgonadotropin, follicle stimulating hormone, thyroid stimulating hormoneand leutenizing hormone; physiologically active enzymes such astransferases, hydrolases, lyases, isomerases, phosphatases,glycosidases, superoxide dismutase, factor VIII, plasminogen activators;and other therapeutic agents including protein factors such as epidermalgrowth factor, insulin-like growth factor, tumour necrosis factor,transforming growth factors, fibroblast growth factors, patelet-derivedgrowth factors, erythropoietin, colony stimulating factors, bonemorphogenetic proteins, interleukins and interferons. Exemplarynon-protein macromolecules include polysaccharides, nucleic acidpolymers, and therapeutic secondary metabolites including plant productssuch as vinblastine, vincristine, taxol and the like.

Other exemplary drugs include Aspirin, Diflunisal, Diclofenac,Aceclofenac, Acemetacin, Etodolac, Indometacin, Sulindac, Tolmetin,Ibuprofen, Carprofen, Fenbufen, Fenoprofen, Flurbiprofen, Ketoprofen,Ketorolac, Loxoprofen, Naproxen, Oxaprozin, Tiaprofenic acid, Suprofen,Mefenamic acid, Meclofenamic acid, Lumiracoxib, Oxyphenbutazone,Piroxicam, Lornoxicam, Meloxicam, and Tenoxicam. SteroidalAnti-Inflammatory Drugs include Hydrocortisone, Prednisone,Prednisolone, Methylprednisolone, Dexamethasone, Betamethasone,Triamcinolone, Beclometasone, Fludrocortisone acetate, and Aldosterone.Chemotherapeutic drugs include Doxorubicin and DNA alkylating Agentssuch as Melphalan, Chlorambucil, Dacarbazine, Temozolomide, andStreptozotocin. Antimetabolite drugs include Methotrexate, Pemetrexed,Raltitrexed, Tioguanine, Fludarabine, Pentostatin, Cladribine,Floxuridine, and Gemcitabine. Alkaloid drugs include Vincristine,Vinblastine, Vinorelbine, Vindesine, and Topoisomerase. Inhibitorsinclude Etoposide, Teniposide, Irinotecan, and Topotecan. Taxanesinclude Paclitaxel and Docetaxel. Anticoagulants include Warfarin,Acenocoumarol, Phenprocoumon, Argatroban, and Ximelagatran.

Still other exemplary commercially available drugs include13-cis-Retinoic Acid, 2-CdA, 2-Chlorodeoxyadenosine, 5-Azacitidine,5-Fluorouracil, 5-FU, 6-Mercaptopurine, 6-MP, 6-TG, 6-Thioguanine,Abraxane, Accutane®, Actinomycin-D, Adriamycin®, Adrucil®, Afinitor®,Agrylin®, Ala-Cort®, Aldesleukin, Alemtuzumab, ALIMTA, Alitretinoin,Alkaban-AQ®, Alkeran®, All-transretinoic Acid, Alpha Interferon,Altretamine, Amethopterin, Amifostine, Aminoglutethimide, Anagrelide,Anandron®, Anastrozole, Arabinosylcytosine, Ara-C, Aranesp®, Aredia®,Arimidex®, Aromasin®, Arranon®, Arsenic Trioxide, Asparaginase, ATRA,Avastin®, Azacitidine, BCG, BCNU, Bendamustine, Bevacizumab, Bexarotene,BEXXAR®, Bicalutamide, BiCNU, Blenoxane®, Bleomycin, Bortezomib,Busulfan, Busulfex®, C225, Calcium Leucovorin, Campath®, Camptosar®,Camptothecin-11, Capecitabine, Carac™, Carboplatin, Carmustine,Carmustine Wafer, Casodex®, CC-5013, CCI-779, CCNU, CDDP, CeeNU,Cerubidine®, Cetuximab, Chlorambucil, Cisplatin, Citrovorum Factor,Cladribine, Cortisone, Cosmegen®, CPT-11, Cyclophosphamide, Cytadren®,Cytarabine, Cytarabine Liposomal, Cytosar-U®, Cytoxan®, Dacarbazine,Dacogen, Dactinomycin, Darbepoetin Alfa, Dasatinib, Daunomycin,Daunorubicin, Daunorubicin Hydrochloride, Daunorubicin Liposomal,DaunoXome®, Decadron, Decitabine, Delta-Cortef®, Deltasone®, DenileukinDiftitox, DepoCyt™, Dexamethasone, Dexamethasone Acetate, DexamethasoneSodium Phosphate Dexasone, Dexrazoxane, DHAD, DIC, Diodex, Docetaxel,Doxil®, Doxorubicin, Doxorubicin Liposomal, Droxia™, DTIC, DTIC-Dome®,Duralone®, Efudex®, Eligard™, Ellence™, Eloxatin™, Elspar®, Emcyt®,Epirubicin, Epoetin Alfa, Erbitux, Erlotinib, Erwinia L-asparaginase,Estramustine, Ethyol, Etopophos®, Etoposide, Etoposide Phosphate,Eulexin®, Everolimus, Evista®, Exemestane, Fareston®, Faslodex®,Femara®, Filgrastim, Floxuridine, Fludara®, Fludarabine, Fluoroplex®,Fluorouracil, Fluorouracil (cream), Fluoxymesterone, Flutamide, FolinicAcid, FUDR®, Fulvestrant, G-CSF, Gefitinib, Gemcitabine, Gemtuzumabozogamicin, Gemzar, Gleevec™, Gliadel® Wafer, GM-CSF, Goserelin,Granulocyte—Colony Stimulating Factor, Granulocyte Macrophage ColonyStimulating Factor, Halotestin®, Herceptin®, Hexadrol, Hexylen®,Hexamethylmelamine, HMM, Hycamtin®, Hydrea®, Hydrocort Acetate®,Hydrocortisone, Hydrocortisone Sodium Phosphate, Hydrocortisone SodiumSuccinate, Hydrocortone Phosphate, Hydroxyurea, Ibritumomab, IbritumomabTiuxetan Idamycin®, Idarubicin, Ifex®, IFN-alpha Ifosfamide, IL-11 IL-2Imatinib mesylate, Imidazole Carboxamide Interferon alfa, InterferonAlfa-2b (PEG Conjugate), Interleukin-2, Interleukin-11, Intron A®(interferon alfa-2b), Iressa®, Irinotecan, Isotretinoin, Ixabepilone,Ixempra™, K Kidrolase (t), Lanacort®, Lapatinib, L-asparaginase, LCR,Lenalidomide, Letrozole, Leucovorin, Leukeran, Leukine™, Leuprolide,Leurocristine, Leustatin™, Liposomal Ara-C, Liquid Pred®, Lomustine,L-PAM, L-Sarcolysin, Lupron®, Lupron Depot®, Matulane®, Maxidex,Mechlorethamine, Mechlorethamine Hydrochloride, Medralone®, Medrol®,Megace®, Megestrol, Megestrol Acetate, Melphalan, Mercaptopurine, Mesna,Mesnex™ Methotrexate, Methotrexate Sodium, Methylprednisolone,Meticorten®, Mitomycin, Mitomycin-C, Mitoxantrone, M-Prednisol®, MTC,MTX, Mustargen®, Mustine Mutamycin®, Myleran®, Mylocel™, Mylotarg®,Navelbine®, Nelarabine, Neosar®, Neulasta™, Neumega®, Neupogen®,Nexavar®, Nilandron®, Nilutamide, Nipent®, Nitrogen Mustard, Novaldex®,Novantrone®, Octreotide, Octreotide acetate, Oncospar®, Oncovin®,Ontak®, Onxal™, Oprevelkin, Orapred®, Orasone®, Oxaliplatin, Paclitaxel,Paclitaxel Protein-bound, Pamidronate, Panitumumab, Panretin®,Paraplatin®, Pediapred®, PEG Interferon, Pegaspargase, Pegfilgrastim,PEG-INTRON™, PEG-L-asparaginase, PEMETREXED, Pentostatin, PhenylalanineMustard, Platinol®, Platinol-AQ®, Prednisolone, Prednisone, Prelone®,Procarbazine, PROCRIT®, Proleukin®, Prolifeprospan 20 with CarmustineImplant, Purinethol®, Raloxifene, Revlimid®, Rheumatrex®, Rituxan®,Rituximab, Roferon-A® (Interferon Alfa-2a) Rubex®, Rubidomycinhydrochloride, Sandostatin®, Sandostatin LAR®, Sargramostim,Solu-Cortef®, Solu-Medrol®, Sorafenib, SPRYCEL™, STI-571, Streptozocin,SU11248, Sunitinib, Sutent®, Tamoxifen, Tarceva®, Targretin®, Taxol®,Taxotere®, Temodar®, Temozolomide, Temsirolimus, Teniposide, TESPA,Thalidomide, Thalomid®, TheraCys®, Thioguanine, Thioguanine Tabloid®,Thiophosphoamide, Thioplex®, Thiotepa, TICE®, Toposar®, Topotecan,Toremifene, Torisel®, Tositumomab, Trastuzumab, Treanda®, Tretinoin,Trexall™, Trisenox®, TSPA, TYKERB®, VCR, Vectibix™, Velban®, Velcade®,VePesid®, Vesanoid®, Viadur™, Vidaza®, Vinblastine, Vinblastine Sulfate,Vincasar Pfs®, Vincristine, Vinorelbine, Vinorelbine tartrate, VLB,VM-26, Vorinostat, VP-16, Vumon®, Xeloda®, Zanosar®, Zevalin™,Zinecard®, Zoladex®, Zoledronic acid, Zolinza, and Zometa.

A method of preparing a star polymer occlusion complex comprises i)forming a mixture of an amphiphilic star polymer and a cargo material ina first solvent; and ii) injecting the mixture into a second solvent,the second solvent being a non-solvent for the cargo material, therebyforming a star polymer occlusion complex; wherein the star polymercomprises a crosslinked polymer core and 6 or more independent polymerarms covalently linked to the core, the 6 or more polymer arms eachcomprise a hydrophobic chain segment and a hydrophilic chain segment. Inan embodiment, the star polymer comprises no more than 100 ppm of anysingle restricted metal.

Nanoshells.

The nanoshells preferably have an average particle size of about 15 nmto about 300 nm, about 20 nm to about 300 nm, or more particularly about20 nm to about 100 nm, as measured by electon microscopy (SEM and TEM)and/or light scattering measurements.

The nanoshells preferably have a polydispersity index of 2 to 1, moreparticularly 1.3 to 1 as measured by electon microscopy (SEM and TEM)and/or light scattering measurements.

A nanoshell can be prepared by disposing a shell-forming material on aunimolecular star polymer occlusion complex. Alternatively, a nanoshellcan be prepared by disposing a shell material on an aggregate of two ormore macromolecules of star polymer occlusion complex. FIG. 2schematically shows exemplary reaction pathways for forming silicananoshells, iron oxide nanoshells, or gold nanoshells using a commonunimolecular star polymer occlusion complexes comprising a porphyrin dye(e.g., DTBP) cargo material. In a first reaction pathway, a silicananoshell is formed by treating the star polymer occlusion complex withan organosilicate. The silica-containing shell can be contiguous (shown)or non-contiguous (not shown). In a second reaction, an iron oxidenanoshell is formed by depositing pre-formed iron oxide nanoparticles onthe star polymer occlusion complex. The iron oxide nanoparticles remaindiscrete particles in association with the peripheral hydrophilic chainsegments of the star polymer arms. Thus, in this example, the iron oxideshell is non-contiguous. In a third reaction pathway of FIG. 2, a goldnanoshell is formed by i) treating the star polymer occlusion complexwith pre-formed gold seeds, thereby forming a seeded occlusion complex,and ii) subjecting the seeded occlusion complex to a growth stepemploying electroless gold deposition, thereby forming a shell thatincludes gold. The gold-containing shell can be non-contiguous (notshown) depending on the conditions of the growth step.

The shell contacts at least one peripheral hydrophilic chain segment ofthe star polymer occlusion complex. The thickness of the shell can beadjusted by changing three parameters: reaction time, size of starpolymer occlusion complex, and concentration of the shell-forminginorganic material. The shell can encompass one or more macromoleculesof star polymer occlusion complex. The one or more macromolecules ofstar polymer occlusion complex can be in an aggregated or non-aggregatedstate.

The nanoshells can be further modified to introduce reactive or passivesurface functionality using one or more organic tagging agents such as,for example, reactive dyes and/or reactive polymers comprisingpoly(alkylene oxide) chain segments (e.g., a poly(ethylene oxide) havingone reactive end group). The organic tagging agent can react with theshell material to form an organic surface group covalently linked to theshell surface. The organic surface group can comprise a chemical moietyselected from the group consisting of dye moieties, polymers comprisingpoly(alkylene oxide) chain fragments, and combinations thereof derivedfrom the tagging agent. As another example, the nanoshell surface can bemodified by incorporating organic surface groups capable of targetingspecific cell types. In this manner, multi-functional nanoshells can beformed. That is, a cargo material can perform a first function, and oneor more covalently bound organic surface groups can perform one or moreother functions. The shell material can perform an additional function.

A discussion of more specific nanoshells follows.

Silica Nanoshells.

Unless otherwise stated, the term “silica nanoshell” herein refers to ananoshell comprising a shell comprising a tetravalent silicon material.The tetravalent silicon can be in the form of a silicon oxide (e.g.,silica) and/or another tetravalent silicon material. Two highlyreproducible methods are disclosed for forming silica nanoshells, whichare illustrated in the reaction schemes of FIGS. 10A and 10B.

In a first method, referred to as a “two pot” method exemplified in FIG.10A, a star polymer occlusion complex is treated with a first siliconagent in a first solvent, and the resulting precursor nanoshell istransferred to a second solvent before adding a second silicon agent toform the silicon nanoshell. The method comprises i) treating the starpolymer occlusion complex with a first silicon agent in a first solvent,thereby forming a precursor nanoshell and ii) treating the precursornanoshell in a second solvent with a second silicon agent, therebyforming the nanoshell.

In a second method, referred to as a “one pot” method (FIG. 10B), a starpolymer occlusion complex is treated sequentially with a first siliconagent and a second silicon agent using a common solvent and one reactionvessel. The method comprises i) treating a star polymer occlusioncomplex with a first silicon agent in a solvent, thereby forming aprecursor nanoshell and ii) treating the precursor nanoshell with asecond silicon agent in the solvent, thereby forming a siliconnanoshell.

Exemplary first silicon agents include orthosilicates of the formulaH_(n)Si(OR)_(4-n) wherein n is an integer of 0 to 2, and R is amonovalent radical selected from alkyl, alkenyl, alkynyl, aryl,alkyl-substituted aryl, alkenyl-substituted aryl, alkynyl-substitutedaryl, aryl-substituted alkyl, alkenyl-substituted alkyl, oralkynyl-substituted alkyl, or combinations thereof. More specificexamples of first silicon agents include tetramethyl orthosilicate(TMOS), tetraethyl orthosilicate (TEOS), tetrapropyl orthosilicate,tetraisopropyl orthosilicate, tetraallyl orthosilicate,tetrakis(2-hydroxyethyl), tetrabutyl orthosilicate, tetraamylorthosilicate, tetrahexyl orthosilicate, tetraoctyl orthosilicate,tetraphenyl orthosilicate, tetratolyl orthosilicate,tetrakis(2-ethyl-1-butyl) orthosilicate, tetrakis(2-methoxyethyl)orthosilicate, and tetrakis(dimethylsilyl) orthosilicate.

Exemplary second silicon agents include compounds of the formulaHN(SiR₃)₂ wherein R is a monovalent radical selected from alkyl,alkenyl, alkynyl, aryl, alkyl-substituted aryl, alkenyl-substitutedaryl, alkynyl-substituted aryl, aryl-substituted alkyl,alkenyl-substituted alkyl, alkynyl-substituted alkyl, or combinationsthereof. Specific examples include hexamethyldisilazane (HMDS) andhexaethyldisilazane. Other second silicon agents include functionalizedorganosilanes of the formula R₂Si(OR)₂, wherein each R is a monovalentradical independently selected from alkyl, alkenyl, alkynyl, aryl,alkyl-substituted aryl, alkenyl-substituted aryl, alkynyl-substitutedaryl, aryl-substituted alkyl, alkenyl-substituted alkyl,alkynyl-substituted alkyl, halo substituted versions of any of theforegoing functionalized organosilanes, or combinations thereof.Specific examples include diphenyldimethoxysilane,diethyldimethoxysilane, dimethyldimethoxysilane, anddimethoxy-methyl(3,3,3-trifluoropropyl)silane. Other second siliconagents include halosilanes and dihalosilanes, such as for example,chlorotrimethylsilane and dichlorodimethylsilane.

The second silicon agent can serve as a surface passivating agent or anagent for introducing a reactive functionality, such as an amine.Exemplary second silicon agents for introducing surface primary aminegroups include aminopropyltrimethoxysilane (APTMS) andaminopropyldimethylethoxysilane (APDMES).

The silicon nanoshells can be treated with one or more organic taggingagents to form tagged silicon nanoshells comprising organic surfacegroups derived from the tagging agent which are covalently linked to theshell surface. The surface groups can comprise an organic moietyselected from the group consisting of dyes, poly(alkylene oxide) chainsegments, poly(alkylene imine) chain segments, biologically activemoieties, and combinations thereof. Biologically active moieties includeproteins, drugs, and compounds comprising functional groups capable ofspecific cell recognition. Exemplary organic tagging agents capable ofreacting with nucleophilic groups (e.g., amines, thiols, alcohols) ofthe silicon nanoshell surface include electrophilic materials such asPEGylating reagents (i.e., a poly(ethylene glycol) having a reactive endgroup capable of reacting with an amine, thiol or alcohol to form acovalent bond, which are commercially available in a variety ofpolyether molecular weights. Other electrophilic tagging agents includeelectrophilic dyes, such as dansyl chloride.

Metal Nanoshells.

A method of forming a metal nanoshell comprises i) treating a starpolymer occlusion complex with a pre-formed seed particle comprising afirst metal, thereby forming a seeded occlusion complex and/or ii)depositing by electroless deposition on the seeded occlusion complex asecond metal from a salt of the second metal, thereby forming a metalnanoshell. The metal nanoshell comprises a metal-containing shelldisposed on one more star polymer occlusion complex macromolecules. Thefirst metal and the second metal can be the same metal or differentmetals. The pre-formed seed and the shell can comprise ionic and/ornonionic forms of the metal. The metal-containing shell can becontiguous or noncontiguous, porous or non-porous.

The first metal and the second metal can be independently selected fromthe group consisting of gold, silver, platinum, tin, copper, nickel,palladium, zinc, iron, titanium, aluminum, and combinations thereof. Inan embodiment, the first metal and the second metal comprise gold.

Iron Oxide Nanoshells.

A first method of forming an iron oxide nanoshell comprises treating astar polymer occlusion complex with a pre-formed iron oxide particles,thereby forming a iron oxide nanoshell, the iron oxide nanoshellcomprising the iron oxide nanoparticles bound by non-covalentinteractions with a hydrophilic chain segment of the star polymerocclusion complex.

A second method of forming an iron oxide nanoshell comprises treating astar polymer with mixture comprising i) a solvent, ii) a cargo materialdissolved in the solvent and iii) a pre-formed iron oxide particlessuspended in the solvent, thereby forming a iron oxide nanoshell,wherein the iron oxide nanoshell comprises i) the star polymer, ii) thecargo material bound by non-covalent interaction to a hydrophobic chainsegment of the star polymer, and iii) the iron oxide nanoparticles boundby non-covalent interactions with a hydrophilic chain segment of thestar polymer.

Also disclosed are aqueous mixtures comprising a nanoshell, wherein thenanoshell comprises a shell material disposed on one or more starpolymers and/or one or more macromolecules of the star polymer occlusioncomplex. The star polymer occlusion complex comprises a cargo materialand a star polymer, the star polymer comprising a crosslinked polymercore and 6 or more independent polymer arms covalently linked to thecore, the polymer arms comprising a peripheral hydrophilic polymer chainsegment and an inner hydrophobic polymer chain segment, the star polymercomprising no more than 100 ppm of any single restricted metal, thecargo material in contact with the polymer core and/or with one or moreof the polymer arms. In an embodiment, the shell material comprisessilicon, iron, or gold. In an embodiment the cargo material is an imagecontrast enhancing material. In another embodiment, the contrastenhancing material is a porphyrinoid compound. In another embodiment,the contrast enhancing material is selected from the group consisting of

and combinations thereof.In another embodiment, 10% to 100% of the image enhancing material isnot aggregated in the star polymer occlusion complex. In anotherembodiment, 50% to 100% of the image enhancing material is notaggregated in the star polymer occlusion complex.

INDUSTRIAL APPLICATIONS

Further disclosed is a method of treating a cell, comprising contactingthe cell with an aqueous mixture comprising the above describednanoshells. The biologically active cargo can comprise a singlebiologically active material or a mixture of biologically activematerials. The biologically active material can be a substance selectedfrom the group consisting of drugs, genes, dyes, image contrastenhancing materials, and combinations thereof. The biologically activecargo can be a drug, for example doxorubicin. In an embodiment, thebiologically active material is a porphyrinoid compound. Cells can becontacted in vitro, ex vivo, or in vivo. Contacting preferably induces0% to 20%, 0% to 15%, 0% to 10%, 0% to 5%, 0% to 2%, or moreparticularly 0% to 1% cytotoxicity. In an embodiment, contacting inducesno cytotoxicity.

No restriction is placed on the type of cell that can be treated withthe above-described star polymer occlusion complexes. In particular, thecells can be eukaryotic cells, mammalian cells, and more particularlyrodent or human cells. The cells can be derived from various tissues,including extraembryonic or embryonic stem cells, totipotent orpluripotent, dividing or non-dividing, parenchyma or epithelium,immortalized or transformed, or the like. The cell may be a stem cell ora differentiated cell. Cell types that are differentiated includeadipocytes, fibroblasts, myocytes, cardiomyocytes, endothelium,dendritic cells, neurons, glia, mast cells, blood cells and leukocytes(e.g., erythrocytes, megakaryotes, lymphocytes, such as B, T and naturalkiller cells, macrophages, neutrophils, eosinophils, basophils,platelets, granulocytes), epithelial cells, keratinocytes, chondrocytes,osteoblasts, osteoclasts, hepatocytes, and cells of the endocrine orexocrine glands, as well as sensory cells.

The above-described nanoshells can be used as non-viral transfectionvectors. The target gene is not limited to any particular type of targetgene or nucleotide sequence. For example, the target gene can be acellular gene, an endogenous gene, an oncogene, a transgene, or a viralgene including translated and non-translated RNAs. Exemplary possibletarget genes include: transcription factors and developmental genes(e.g., adhesion molecules, cyclin-dependent kinase inhibitors, Wntfamily members, Pax family members, Winged helix family members, Hoxfamily members, cytokines/lymphokines and their receptors,growth/differentiation factors and their receptors, neurotransmittersand their receptors); oncogenes (e.g., ABLI, BCLI, BCL2, BCL6, CBFA2,CBL, CSFIR, ERBA, ERBB, ERBB2, ETSI, ETV6, FGR, FOS, FYN, HCR, HRAS,JUN, KRAS, LCK, LYN, MDM2, MLL, MYB, MYC, MYCLI, MYCN, NRAS, PIMI, PML,RET, SKP2, SRC, TALI, TCL3, and YES); tumor suppressor genes (e.g., APC,BRAI, BRCA2, CTMP, MADH4, MCC, NF1, NF2, RB1, TP53, and WTI); andenzymes (e.g., ACP desaturases and hydroxylases, ADP-glucosepyrophorylases, ATPases, alcohol dehydrogenases, amylases,amyloglucosidases, catalases, cyclooxygenases, decarboxylases,dextrinases, DNA and RNA polymerases, galactosidases, glucose oxidases,GTPases, helicases, integrases, insulinases, invertases, isomerases,kinases, lactases, lipases, lipoxygenases, lysozymes, peroxidases,phosphatases, phospholipases, phosphorylases, proteinases andpeptidases, recombinases, reverse transcriptases, telomerase, includingRNA and/or protein components, and topoisomerases).

The preparation and use of star polymers, star polymer occlusioncomplexes, and nanoshells is further illustrated by the followingexamples.

EXAMPLES

Materials used in the following examples are listed in Table 6.

TABLE 6 Abbreviation Description Source Alpha-Methoxy-Omega-CarboxylicAcid Iris Biotech Succinimidyl Ester Poly(Ethylene GmbH Glycol); PEG MW750 Dalton Alpha-Methoxy-Omega-Carboxylic Acid Iris Biotech SuccinimidylEster Poly(Ethylene GmbH Glycol); PEG MW 2000 DaltonAlpha-Methoxy-Omega-Carboxylic Acid Iris Biotech Succinimidyl EsterPoly(Ethylene GmbH Glycol); PEG MW 5000 DaltonAlpha-Methoxy-Omega-Carboxylic Acid Iris Biotech Succinimidyl EsterPoly(Ethylene GmbH Glycol) PEG MW 10000 DaltonAlpha-Methoxy-Omega-Mercapto Iris Biotech Poly(Ethylene Glycol); PEG MW5000 GmbH Dalton DMAEMA 2-(N,N-Dimethylamino)Ethyl Sigma AldrichMethacrylate APTMS 3-Aminopropyltrimethoxy Silane Sigma Aldrich APDMES3-Aminoproplyldimethylethoxysilane Sigma Aldrich DPDMSDiphenyldimethoxysilane Sigma Aldrich TEOS Tetraethylorthosilicate SigmaAldrich TMOS Tetramethylorthosilicate Sigma Aldrich DTBP5,10,15,20-(3,5- Synthesized Ditertbutylphenyl)Porphyrin according toliterature proceedure below DANSYL-Cl5-Dimethylaminonaphthalen-1-Sulfonyl Sigma Aldrich Chloride DPDMSDiphenyldimethoxysilane Gelest HMDS Hexamethyldisilazane Sigma AldrichTHF Tetrahydrofuran Sigma Aldrich 3-(t-Butyldimethylsilyloxy)-1-PropylFMC Lithium Lithium Division Bu₄N⁺F⁻ Tetrabutylammonium Fluoride SigmaAldrich 2-Bromoisobutyryl Bromide Sigma Aldrich Hydroxylamine Amine HClSigma Aldrich THPC Tetrakis(Hydroxymethyl)Phosphonium Sigma AldrichChloride Gold (III) Chloride Sigma Aldrich Iron(III)Acetylacetone SigmaAldrich 30% Ammonium hydroxide JT Baker BOD 4-4′-Bioxepanyl-7,7′-dioneTCI America BNPEG Boc-protected amino-poly(ethylene Iris Biotech glycol)(Mn = 5000) GmbH TBD 1,5,7-Triazabicyclo[4.4.0]dec-5-ene Sigma Aldrich(organocatalyst)

Instrumentation. ¹H NMR spectra were obtained on a Bruker Avance 2000spectrometer (400 MHz) using 5 mm o.d. tubes and were referenced tointernal solvent residue (¹H, CDCl₃: delta=7.24). Analytical GelPermeation Chromatography (GPC) using Waters high resolution columnsHR1, HR2, HR4E and HR5E (flow rate 1 mL/min, THF) was used to determinemolecular weight distributions, M_(w)/M_(n), of polymer samples withrespect to linear polystyrene standards. Absorption studies wereperformed using a 8453 Agilent UV-VIS spectrophotomer. Nanoshells werespin-coated on a silicon wafer at 3000 rpms and were dried on athermoplate for one minute at 110° C. prior to characterization using aHitachi S-4700 cold field emission scanning electron microscope. Thenanoshells were deposited on copper grids and dried under vacuum forfurther characterization using a Topcon 002B transmission electronmicroscope running at 200 kV.

Star Polymer.

The star polymers used in the following examples had a hydrodynamicradius of 19 nm and each polymer contained approximately 33 arms made ofa polystyrene core (3 kDa), and a dimethylaminoethylmethacrylate arm ofeither (6 or 8 kDa). The hydrophobic polystyrene core is capable ofsequestering hydrophobic organic dyes and the polyamine shell providesboth water solubility and nucleation sites for the template.Non-aggregating porphyrin dyes were selected to use in this work owingto their strong absorption profile across a wide section of the UV-VISspectrum.

The star polymer architecture used in forming the occlusion complexesbelow with a hydrophobic cargo material has i) a crosslinked hydrophobiccore, ii) at least 6 independent arms covalently bound at one end to thehydrophobic core, wherein the arms comprise a) respective innerhydrophobic segments bound to the core and b) respective peripheralhydrophilic segments attached to the inner hydrophobic segments, andiii) a plurality of functionalities along the peripheral hydrophilicsegments of the arms to facilitate interaction with a specific inorganicnanoshell precursor. More specifically, the star polymers prepared inthe following examples comprise a crosslinked polystyrene core and about33 arms comprising respective inner hydrophobic segments of polystyreneand respective peripheral hydrophilic segments comprisingpoly(2-(N,N-dimethylamino)ethyl methacrylate) (DMAEMA)

Preparation of Star Polymer SP-1.

(A). Synthesis of Precursor 1, a “Protected”3-(tert-butyldimethylsilyloxy)-1-propyl Terminated Polystyrene StarPolymer (Typical Procedure).

3-(t-Butyldimethylsilyloxy)-1-propyl lithium (0.60 mL, 20 wt. % solutionin cyclohexane) was added to a stirred solution of styrene (12.00 mL) ina cyclohexane (200 mL) and THF (10 mL) mixture under an argonatmosphere. After 20 min an aliquot (approximately 2 mL) was taken,quenched in degassed MeOH (approx. 150 mL) and a representative sampleof the “free” polystyrene arm collected by filtration. A mixture ofp-divinylbenzene (2.70 mL) and styrene (0.12 mL) in cyclohexane (3.00mL) was added and the reaction mixture stirred for a further 40 min. Thereaction solution was then quenched by slow addition to a rapidlystirred solution of MeOH and EtOH (1.5 L, 1:1). The precipitate formedwas isolated by filtration and air dried to a constant weight. The crudestar-polymer was then dissolved in CH₂Cl₂ (100 mL) before the slowaddition of acetone (150 mL) and then isopropyl alcohol (30 mL). Thesolution was allowed to stand until the product formed a substantialoily layer on the bottom of the container. The mixture was decantedallowing isolation of the oil which was then dried in a vacuum oven toconstant weight affording the “protected” intermediate star polymer(Precursor 1) (9.5 g). ¹H NMR (400 MHz, CDCl₃) delta=0.18 (br s, 6H)0.85 (br s, 9H), 1.44 (br s, 330H) 1.85 (br s, 165 H), 3.35 (br s, 2H)6.50-6.60 (br m, 330H), 7.10 (br s, 495H). Analytical GPC:M_(w)/M_(n)=1.15. Light Scattering: M_(w)=600 000 g/mol,M_(w)/M_(n)=1.09, R_(h)(avg) 10.8 nm. ¹H NMR (400 MHz, CDCl₃) analysisof the “free arm” sample indicated arm length of approx. 165 repeatunits. This implied the approximate number of “arms” in the star-polymerwas about 36.

(B). Synthesis of Precursor 2, a “Deprotected” Hydroxy-TerminatedPolystyrene Star Polymer (Typical Procedure).

Precursor 1 (9.0 g) was dissolved in THF (9.0 mL) and tetrabutylammoniumfluoride (1.0 M solution in THF, 9.0 mL) was added. The reactionsolution was stirred for 60 hours at room temperature before beingwarmed to 50° C. for 1 hour. The solution was allowed to cool to roomtemperature before it was slowly added to MeOH (1 L) with rapidstirring. The precipitate formed was isolated by filtration and airdried to a constant weight to afford the “deprotected” Precursor 2 (8.5g). ¹H NMR (400 MHz, CDCl₃) delta=1.44 (br s, 330H) 1.85 (br s, 165H),3.45 (br s, 2H) 6.50-6.60 (br m, 330H), 7.10 (br s, 495H). AnalyticalGPC: M_(w)/M_(n)=1.14. Light Scattering: M_(w)=608 000 g/mol,M_(w)/M_(n)=1.14, R_(h)(THF, average) 10.6 nm.

(C). Synthesis of Precursor 3, a Polystyrene Star Polymer PeripherallyFunctionalized with Atom Transfer Radical Polymerization(ATRP)-Initiator Moiety.

A solution of 2-bromoisobutyryl bromide (1.4 g, 4 equivalents per starpolymer alcohol end group) in anhydrous dichloromethane (30 mL) wasadded dropwise over 15 minutes to a solution of hydroxy star polymerPrecursor 2 (5.0 g) and triethylamine (0.75 g) in anhydrousdichloromethane (30 mL) at 0° C. The mixture was allowed to warm up toroom temperature for 14 hours, then heated to a gentle reflux for 4hours. Pure product Precursor 3 was obtained after repeatedprecipitation into methanol. GPC and DLS analysis showed no significantchange from that of the hydroxy star polymer starting material. ¹H NMR(CDCl₃, 4000 MHz) characterization of the product confirmed quantitativeend-group transformation.

(D). Synthesis of SP-1, a Polystyrene Star Polymer Terminated withPoly(2-(N,N-Dimethylamino)Ethyl Methacrylate) (DMAEMA)

ATRP-initiator peripherally functional polystyrene (PS) star polymerPrecursor 3 (0.3 g), N,N-dimethylaminoethylmethacrylate (DMAEMA) (2.3g), copper(I) chloride (5.4 mg) and 4,4′-nonyl-2,2′-bipyridine (45.0 mg)were dissolved in toluene (5.0 mL). The solution was degassed and sealedunder a nitrogen atmosphere before being heated to 90° C. for 15 hours.The reaction solution was then cooled and added to hexane (50 mL) withrapid stirring. The precipitate thus formed was isolated, dissolved inmethylene chloride and again added to hexane (50 mL) with rapidstirring. The precipitate thus formed was isolated and air dried to aconstant weight to produce star polymer SP-1 (0.4 g) as a white solid.¹H NMR (400 MHz, CDCl₃) delta (ppm)=0.78 (br, s, 6H), 0.90 (br s, 40H),1.08 (br s, 20H), 1.45 (br s, 60H), 1.86 (br s, 80H), 2.33 (br s, 120H),2.63 (br s 40), 4.11 (br s, 40), 6.50-6.60 (br m, 66H), 7.13 (br s,99H). DLS (THF): M_(w)=190,000 g/mol, M_(w)/M_(n)=1.05, hydrodynamicradius R_(h(avg))=8.5 nm.

Preparation of Star Polymer SP-2.

The above described procedure for SP-1 was used to prepare star polymerSP-2, using DMAEMA (2.6 g) and 60 min reaction time.

Preparation of Star Polymer SP-3.

The above described procedure for SP-1 was used to prepare star polymerSP-3, using DMAEMA (2.6 g) and 85 min reaction time.

Table 7 summarizes the properties of SP-1, SP-2 and SP-3. “PS component”and “DMAEMA component” in Table 7 refer to the average molecular weightof these components in the star polymer, as determined by NMR. Radius“d” refers to the hydrodynamic radius as determined by light scattering.

TABLE 7 Light MW (kDa) by NMR Scattering Sam- # of PS DMAEMA MW RadiusGPC ple Arms Star component component (kDa) d (nm) (PDI) SP-1 33 231 3.33.7 190 18 1.12 SP-2 33 211 3.3 3.1 274 22 1.16 SP-3 33 320 3.3 6.4 28323.6 1.17

General Procedure for Preparation of Star Polymer Occlusion Complex.

As shown in the schematic reaction diagram of FIG. 2, a star polymerocclusion complex comprises a cargo material occluded in a star polymer.The cargo material can be bound by non-covalent interactions or covalentinteractions. In this example the cargo is a hydrophobic dye. Forillustration purposes not meant to be limiting, the molecular structuredepicted in FIG. 2 shows three molecules of a dye occluded in the starpolymer. The number of occluded molecules of cargo material can be oneor more. The hydrophobic dye is believed to be in contact with the innerhydrophobic segment of the polymer arms and the hydrophobic core.

The following general procedure employs hydrophobic solvatochromic dyesas representative therapeutically useful materials (e.g.,pharmaceuticals) to prepare water based star polymer occlusioncomplexes. The nanoparticles of amphiphilic star polymers are occludedwith the dye using hydrophobic/hydrophilic interactions. A solution wasprepared containing hydrophobic dye material (5 mg) and star-polymer(25.0 mg, approximately 0.1 micromoles) in THF (0.1 mL, about 10 mM).The solution was added dropwise to water (0.9 mL) with rapid stirring,causing the water to rapidly and uniformly color from the dye. Excesssolid dye material not adsorbed to the star polymer was removed bypassing the mixture through a 0.45 micrometer syringe filter, therebyforming a clear and uniformly colored aqueous solution. Residual THF wasremoved under vacuum. The further addition of water had no visibleeffect on the homogeneity of the solution. Ultraviolet-visible (UV-VIS)absorption spectra of the aqueous formulations containing the varioussolvatochromic dye materials were used to demonstrate the association ofthese model hydrophobic materials with the star polymer in the aqueousenvironment.

Preparation of Occlusion Complex, OC-1, with Porphyrin Dye DTBP.

The above-described procedure was used to prepare star polymer occlusioncomplex OC-1 from star polymer SP-1 and5,10,15,20-(3,5-ditertbutylphenyl)porphyrin (M=2H) (DTBP).

FIG. 3 is a photograph of side by side vials containing from the left i)the star polymer SP-1 alone in water, ii) the porphyrin dye DTBP alonein water, and iii) the star polymer occlusion complex OC-1. Overlayingeach vial is a three-dimensional drawing of the corresponding material.The left vial containing the star polymer SP-1 in water is clear andcolorless. The middle vial containing the porphyrin dye DTBP in water isclear with the DTBP precipitated and floating on the top of the aqueousphase. The right vial containing the star polymer occlusion complex OC-1in water is clear and has a magenta hue.

Preparation of Inorganic Nanoshells. I. General Preparation of GoldNanoshells:

Gold seeds (1 nm to 3 nm in average diameter) were prepared according toPham et al., Langmuir 2002, 18, pages 4915-4920. In summary, NaOH (4.5mL, 0.2 M) was added into 45.5 mL of Millipore water and the solutionwas stirred for 2 minutes at 600 rpm. Subsequently, 12 microliters of80% tetrakis(hydroxymethyl)phosphonium chloride (THPC) that was dilutedin 1 mL of Millipore water was added to the mixture and stirred foranother 2 minutes. The pH of the solution was about 12. The final stepwas the fast addition of gold (III) chloride (2 mL, 0.029 M). Thesolution changed from colorless to light brown when the gold (III)chloride was added. The resulting solution of gold seeds was stirred foranother 5 minutes. The aqueous solution containing the star polymerocclusion complex (5 mL) was then mixed with an aqueous solution of goldseeds (5 mL). The combined solution was diluted with water (10 mL) andstirred overnight. The solution was dialyzed against water using acellulose dialysis membrane with 12,000 Da to 14,000 Da molecular weightcut-off (MWCO) for 24 hours. The dialyzed solution was stored at 4° C.,thereby producing a gold seeded occlusion complex. A three-dimensionaldrawing representation of the gold seeded occlusion complex formed inthis manner is shown in FIG. 2. A gold (III) chloride solution (0.0955M, 1.74 mL) was diluted with 98.2 mL of Millipore water and potassiumcarbonate (100 mg) was added. The resulting solution was dark aged 24hours to form a gold(III) hydroxide solution for the following growthstep. The gold growth step was initiated by mixing the gold hydroxidesolution (14.8 mL) of the solution of gold seeded occlusion complex (9mL) with vortex agitation at 650 rpm for one minute. The hydroxylaminehydrochloride solution (freshly prepared at 0.026%, 20 mL) was thenadded to the mixture over 45 seconds. The final solution was stirred foranother 15 minutes and stored at 4° C. prior to further purificationsteps. The gold nanoshell solution was dialysed against water for 24hours and then against methanol for 24 hours (cellulose membrane with12,000 Da to 14,000 Da MWCO). The gold nanoshell particles were isolatedby freeze-drying.

The particle size of gold nanoshells depends on the ratio of the volumeof the gold seeded star polymer solution to the volume of thehydroxylamine solution added, the total volume and/or reagentconcentration of the growth solution reagents (i.e., gold hydroxide,gold seeded star polymer solution, and hydroxylamine hydrochloride), andaddition rate of hydroxylamine, as shown below in Table 8 below. Forexample, to achieve an average of 110 nm particles (in diameter), thevolume of gold hydroxide, gold seeded star polymer solution, andhydroxylamine hydrochloride was 14.8 mL, 9 mL, and 20 mL, respectively.

Example 1 Preparation of Gold Nanoshells, AuNS-1

The above described procedure was used to prepare gold nanoshells AuNS-1from star polymer occlusion complex OC-1. The average particle diameterwas 110 nm as determined from SEM images. FIGS. 4A and 4B are SEM imagescomparing commercially available solid gold particles and goldnanoshells AuNS-1, respectively. The particle size in each photograph issimilar, about 110 nm. This particle size is suitable, for example, forsystemic in vivo delivery of a biologically active material such as adrug. Each AuNS-1 nanoparticle is believed to encapsulate multiplemacromolecules of star polymer occlusion complex, as shown in thethree-dimensional drawing representation of FIG. 4B. The photographicinset images in the TEM images of FIGS. 4A and 4B are aqueous solutionsof the solid gold nanoparticles and AuNS-1 nanoparticles, respectively.The solid gold nanoparticle solution in FIG. 4A is magenta. The AuNS-1solution in FIG. 4B is dark blue. FIG. 4C compares the absorptionspectra of the solid gold nanoparticles and AuNS-1. The solid goldnanoparticles have a peak absorbance at 586 nm, whereas AuNS-1 has peakabsorbances at 420 nm (for the porphyrin DTBP) and 778 nm. Only theAuNS-1 solution absorbs in the biological optical window of about 600 nmto more than 1000 nm.

Effects of Changing Various Reaction Parameters.

Different gold nanoshell particle sizes and near infrared (NIR)absorptions can be achieved by modifying synthesis conditions (e.g.,growth solution concentration, seed amount per star polymer and/orgrowth time). The following Examples 2 and 3 demonstrate the effect ofvarying different reaction condition parameters.

Example 2 Preparation of Gold Nanoshells AuNS-2 from SP-1

The above procedure used to form AuNS-1 was also used to form AuNS-2 butusing star polymer SP-1 as the template (rather than its occlusioncomplex OC-1), and using 6 mL of gold seeded star polymer SP-1 solution(rather than 9 ml of OC-1 solution), half the volume of hydroxylaminesolution, and an addition time for the hydroxylamine solution of 20 min.

Example 3 Preparation of Gold Nanoshells AuNS-3 from SP-1

The above procedure used to form AuNS-1 was also used to form AuNS-3,but with 6 mL of gold seeded star polymer occlusion complex OC-1solution, half the volume of hydroxylamine solution, and an additiontime for the hydroxylamine solution of 5 min. Table 8 summarizes theeffects of varying different reaction parameters on the average particlediameter of the gold nanoshells formed.

TABLE 8 Gold Seeded Star Hydroxyl- Hydroxyl- Polymer AuOH amine amineAverage Solution Solution Solution Addition Particle Added Added Addedtime Diameter Sample (mL) (mL) (mg/mL) (min) (nm) Ex. 1 AuNS-1 9 14.85.2/20 0.75 110 Ex. 2 AuNS-2 6 14.8 2.6/10 20 90 Ex. 3 AuNS-3 6 14.82.6/10 5 200

Example 4 Applying a Second Shell to the Gold Nanoshells—Preparation ofGold Nanoshell AuNS-4 from AuNS-2

The gold nanoshells can themselves be used to initiate a second growthstep to provide an additional shell surrounding the original goldnanoshell. For example, gold nanoshell AuNS-4 was formed using the aboveprocedure used to form AuNS-1 but using gold nanoshell AuNS-2 instead ofthe gold “seeded” template OC-1 to provide AuNS-4 with a second,additional gold nanoshell (particle size increased from an average of 90nm for AuNS-2 to an average of 220 nm for AuNS-4).

FIG. 5A is a series of SEMs of AuNS-1 to AuNS-4 having average particlesizes of 90 nm, 110 nm, 200 nm, and 220 nm, respectively. FIG. 5B is agraph showing the partial VIS-NIR absorption curves of AuNS-1 to AuNS-4,showing a red shift in the color of the solutions with increasingparticle size. FIG. 5C is a photograph of the aqueous solutions ofAuNS-1 to AuNS-4, showing a color shift from magenta-purple on the leftto deep blue on the right.

Example 5 Preparation of AuNS-5, a PEGylated Gold Nanoshell from AuNS-1

FIG. 5D is a three-dimensional drawing representation showing thestructure of a gold nanoshell about a star polymer occlusion complexhaving an additional surface coating of functionalized organic materialabout the surface of the gold nanoshell

The gold nanoshells can further be functionalized through the additionof an exterior coating of functionalized organic materials (organictagging agents). For example, gold nanoshell AuNS-1 was contacted insolution with alpha-methoxy-omega-mercapto poly(ethylene glycol)PEGylating agent (PEG MW 5,000 Dalton) as the organic tagging agent toprovide surface modified PEG-functionalized gold nanoshell AuNS-5, whichwas further purified by dialysis (MWCO=14 kDa) against water beforebeing freeze dried to a lyophilized powder. The PEG chain is covalentlylinked to the surface of the tagged nanoshell through the mercapto endgroup. FIG. 5E is a photograph of vials containing PEG functionalizedgold nanoshell AuNS-5 as (left) a lyophilized powder and (right) anaqueous solution. Both the powder and the solution have a blue hue.

Effect of pH.

Aggregation of the star polymer occlusion complex and size of the goldnanoshell can be controlled through pH, as shown in the followingExamples 6 and 7, and in the three dimensional drawing representation ofFIG. 6A. The unimolecular star polymer occlusion complex OC-1 has anaverage particle size of 20 nm to 25 nm.

Example 6 Preparation of Gold Nanoshells, AuNS-6, at pH 3.18

The above procedure used to form AuNS-1 was used to form AuNS-6 but withthe gold seed solution being adjusted to pH 3.18 by the addition ofaqueous HCl prior to the growth step.

Example 7 Preparation of Gold Nanoshells, AuNS-7, at pH 8.4

The above procedure used to form AuNS-1 was used to form AuNS-7 but withthe gold seed solution being adjusted to pH 8.4 by the addition ofaqueous NaOH prior to the growth step.

FIG. 6B is a series of scanning electron micrographs (SEM) of the goldnanoshells AuNS-6 and AuNS-7 prepared in Examples 6 and 7, respectively,and AuNS-1. The average particle size as measured from SEM images ofAuNS-6 was 50 nm. The average particle size of AuNS-7 was 80 nm. Theseare compared to the SEM image of AuNS-1 (prepared with an inherent seedsolution pH of 11.3), which had an average particle size of 110 nm.

Effect of Star Polymer Amine Content.

The size of the gold nanoshell can be controlled through the pendantamine content (DMAEMA) of the star polymer, as shown in the followingExamples 8 and 9. The unimolecular star polymer occlusion complexes OC-1to OC-3 have an average particle size of 18 nm to 24 nm.

Example 8 Preparation of gold nanoshells, AuNS-8 using star polymerSP-2(SP-2 particle diameter of 22 nm, Table 7)

The above procedure used in forming AuNS-1 was used to form AuNS-8 butwith the template being the occlusion complex OC-2 formed from the starpolymer SP-2 (Table 7).

Example 9 Preparation of gold nanoshells, AuNS-9 with star polymer SP-3(SP-3 particle diameter of 24 nm, Table 7)

The above procedure used in forming AuNS-1 was used to form AuNS-9 butwith the template being the occlusion complex OC-3 formed from the starpolymer SP-3 (Table 7). AuNS-9 is believed to contain on average 1 to 2macromolecules of OC-2.

FIG. 7 is a series of scanning electron micrographs (SEM) of the goldnanoshells AuNS-8 (Example 8), AuNS-1, and AuNS-9 (Example 9). Theaverage particle size and polydispersity increase with amine content.The average particle size as of AuNS-8 was 50 nm. AuNS-8 is believed tocontain on average 1 to 2 macromolecules of OC-2. The average particlesize as of AuNS-9 was 120 nm. AuNS-9 was more polydisperse, having aparticle size range of about 50 nm to about 150 nm.

Other Characterizations of Gold Nanoshells.

FIGS. 8A to 8D are images of obtained using various characterizationtechniques used on gold nanoshells AuNS-1. FIG. 8A is an electron energyloss spectrum (EELS) of AuNS-1 showing the periodic presence of carbonand gold in the sample along the line shown on the inserted image,confirming that the bright sections of the nanoparticle containrelatively high proportions of gold and the darker regions containrelatively higher proportions of carbon. The darker regions areapproximately 16 nm to 18 nm in diameter. FIG. 8B is a bright fieldtransmission electron micrograph (BF-TEM) showing the nodulous surfacetopography in greater magnification. FIG. 8C is a high angle annulardark field micrograph obtained with a scanning transmission electronmicroscope (HAADF-STEM), showing another detailed topographical view ofthe AuNS-1 nanoshell. The nodules have a diameter of about 18 nm and arespaced about 16 nm. FIG. 8D is a cross-sectional scanning electronmicrograph of AuNS-1 (cross-sectional sample produced using focusing ionbeam (FIB) milling).

Fluorescence of Gold Nanoshells.

FIG. 9A compares the UV-VIS absorption spectra of star polymer occlusioncomplex OC-1 (single peak at 423 nm) and gold nanoshell AuNS-1 (peaks at419 nm and 790 nm). FIG. 9B compares the fluorescence emission spectraof OC-1 and gold nanoshell AuNS-1 for 420 nm excitation. Thefluorescence of the occluded porphyrin dye in the occlusion complex isretained within the gold nanoshell. The dye is substantially in anon-aggregated state in the star polymer occlusion complex and the goldnanoshell.

II. Preparation of Silicon Nanoshells:

The disclosed star polymers can be engineered to have nucleation sitesin their peripheries. Their ability to form occlusion complexes with avariety of organic dyes provides a versatile alternative template forthe formation of structurally complex silicon based nanoshells.

Synthesis of Silicon Nanoshells Using “Two-Pot” Approach.

FIG. 10A illustrates with molecular models the “Two-Pot” approach toforming silicon nanoshells. In the first step, the appropriate starpolymer (20 mg) and the porphyrin dye DTPB (2 mg) were dissolved in THF(20 microliters). An occlusion complex was made by adding this mixturedrop wise to ethanol (4 mL) with rapid stirring. FIG. 10C is an atomicforce microscope image (AFM) of the star polymer occlusion complex OC-4(Z=10 nm) formed in this manner. This mixture was filtered using apoly(tetrafluoroethylene) (PTFE) filter (0.2 micrometers), and analiquot (2 mL) was added to an aqueous solution of ammonium hydroxide(30% w/v) in ethanol (1:19 v/v, 20 mL). To this solution, 0.15 mL of afirst silicon agent (e.g., TEOS) was added, and the reaction was stirredat room temperature for two hours. The reaction was not allowed toproceed beyond two hours in order to prevent aggregation of theparticles. In step two, the reaction was stopped by the introduction oftoluene (300 mL). The solvent volume was reduced under vacuum at 60° C.,to a final volume of approximately 10 mL. A functionalized organosilane(e.g., hexamethyldisilazane (HMDS)) was then added (1.5 mL) and thereaction stirred for 16 hours at room temperature. The functionalizedsilicon nanoshell thus formed was purified by repeated dialysis againstmethanol (7 kDa cutoff). The hydroxyl group shown in FIG. 10A in step 1represents the residual surface bound silanol OH groups of thenanoparticle's silicate nanoshell.

It is believed that the TEOS reacts with water (catalyzed by the ammoniaand, presumably, by the amines of the star polymer) and begins tocondense with itself. The silanol groups formed on the surface of thecondensing material are relatively acidic compared to the amines foundon the star polymer. Presumably the condensing material is soonelectrostatically attracted to the star polymer at an early stage, thus“seeding” the star polymer prior to continued condensation of the TEOS.

Example 10 Preparation of Silica Nanoshells, SiNS-1

The above “two pot” procedure was used to prepare silica nanoshellsstarting from star polymer occlusion complex OC-4 and HMDS as thefunctional organosilicate as described above. FIG. 10D is a TEM of theSiSN-1 showing a particle size of about 25 nm.

Example 11 Comparison Preparation of Solid Silica Particles

The two pot procedure was used without the star polymer occlusioncomplex to prepare solid silica particles as a comparison example. Theseparticles are shown in FIG. 10E. The particle diameter ranges from about50 nm to 250 nm.

Synthesis of Silica Nanoshells Using “One-Pot” Approach.

The “two pot” methodology was effective, but it was further optimized toa one pot version, where sample handling time was greatly reduced.Furthermore, when a more reactive silicon agent was used, the reactiontime was also significantly reduced.

FIG. 10B illustrates with molecular models the “One-Pot” approach toforming silica nanoshells. In a general procedure, TEOS (21 microliters)was added to a 2 mL aliquot of the star polymer occlusion complex (asdescribed above in the “two-pot” approach) in ethanol (20 mL) and thereaction mixture was stirred at room temperature for 3 hours. Afunctionalized organosilane (e.g., 3-aminoproplyldimethylethoxysilane)was added directly (12 microliters) and the reaction stirred for further16 hours at room temperature. The functionalized silica nanoshells thusformed were purified by repeated dialysis against methanol (7 kDacutoff). The amine group shown in FIG. 10B in step 1 represents theresidual surface bound amine groups of the nanoparticle's shell formedwhen using 3-aminoproplyldimethylethoxysilane as the functionalizedorganosilane component in the reaction.

Example 12 Preparation of Silica Nanoshell, SiSN-2, “One-Pot” Approach

The above described procedure was used to prepare silica nanoshellsSiNS-2 using star polymer occlusion complex OC-4 and3-aminoproplyldimethylethoxysilane as the functionalized organosilicate.FIG. 10F is a SEM of the SiSN-2 nanoshells, which have an averageparticle size of about 30 nm.

Size Control of Silica Nanoshells.

The following Examples 13 to 16 demonstrate that the particle size ofthe silica nanoshells can be controlled through coating time, coatingreagent concentration and/or star polymer size (mixed examples derivedfrom varying these parameters are shown).

Example 13 Preparation of Silica Nanoshells, SiNS-3

The two-pot method as described above for SINS-1 was used to generateSiNS-3 using DPDS as the second organosilicate material. FIG. 11A is aTEM of the SiNS-3 nanoshells, which have an average particle size ofabout 25 nm.

Example 14 Preparation of Silica Nanoshells, SiNS-4

The one-pot method as described above was used to generate SiNS-4 usingDPDS as the second organosilicate material and an extended reactiontime. FIG. 11B is a TEM of the SiNS-4 nanoshells, which have an averageparticle size of about 50 nm.

Example 15 Preparation of Silica Nanoshells, SiNS-5

The one-pot method as described above was used to generate SiNS-5 usingDPDS as the second organosilicate material and 1 ml of ammoniumhydroxide solution.

FIG. 11C is a TEM of the SINS-5 nanoshells, which have an averageparticle size of about 75 nm.

Example 16 Preparation of Silica Nanoshells, SiNS-6

The one-pot method as described above was used to generate SiNS-2 usingDPDS as the second organosilicate material and 1.15 ml of ammoniumhydroxide solution. FIG. 11D is a TEM of the SINS-6 nanoshells, whichhave an average particle size of about 100 nm.

The maximum time for the shell-forming reaction to be completed was twohours before aggregation took place. Therefore, a time line was createdwhere a range of different sizes of silica nanoshells were produced.

Surface Tagging of Silica Nanoshells.

The following examples demonstrate surface tagging of silica nanoshells.Porphyrin occluded star polymers were coated with a silicon-containingshell in a one-pot process using TEOS and the surface of the particleswas treated with aminopropyltrimethoxysilane (APTMS) to introducesurface amine groups. The resulting particles were surface tagged bysequential treatment with an alpha-methoxy-omega-carboxylic acidsuccinimidyl ester poly(ethylene glycol) and dansyl chloride as arepresentative cellular targeting agent. Surface functionalization waschecked by comparing the dansyl and porphyrin components of the UV-VISspectrum before and after extensive dialysis against water. FIG. 12Aschematically shows the sequential tagging reactions.

Example 17 Preparation of Tagged Silica Nanoshell, SiNS-7

Organic tagging agents can be used to modify the surface of thenanoshells. Amino-functionalized SiNS-2 (20 mg) was dissolved in asolution of dichloromethane and triethylamine (9:1) before the additionof alpha-methoxy-omega-carboxylic acid succinimidyl ester poly(ethyleneglycol) having a PEG average molecular weight of 750 Da (0.2 g) as anorganic tagging agent to the reaction solution. The reaction solutionwas then stirred at room temperature for 24 hours before the addition ofdansyl chloride (0.2 g) as a second organic tagging agent and thereaction solution was then stirred for a further 24 hours before beingpurified by dialysis (MWCO=15 kDa) against MeOH and then water. Theresulting solution was freeze dried to afford SiSN-7 as a powder.

Example 18 Preparation of Tagged Silica Nanoshell, SiNS-8

The above described procedure for SiNS-7 was used to prepare taggedsilica nanoshell, SiNS-8 using alpha-methoxy-omega-carboxylic acidsuccinimidyl ester poly(ethylene glycol) having a PEG average molecularweight of 2000 Da as the organic tagging agent.

Example 19 Preparation of Tagged Silica Nanoshell, SiNS-9

The above described procedure for SiNS-7 was used to prepare taggedsilica nanoshell, SiNS-9 using alpha-methoxy-omega-carboxylic acidsuccinimidyl ester poly(ethylene glycol) having a PEG chain averagemolecular weight of 5,000 Da as the organic tagging agent.

Example 20 Preparation of Tagged Silica Nanoshell, SiNS-10

The above described procedure for SiNS-7 was used to prepare taggedsilica nanoshell, SINS-10 using alpha-methoxy-omega-carboxylic acidsuccinimidyl ester poly(ethylene glycol) having a PEG average molecularweight of 10,000 Da as the organic tagging agent.

FIG. 12B compares the absorption curves of the PEGylated and dansylatedsilica nanoshells SiNS-7 to SiNS-10 (Examples 17 to 20). Dansyl chloridehas a peak of about 380 nm whereas the dansylated silica nanoshells havepeaks of about 320 nm to 340 nm. FIG. 12C is a TEM of tagged silicananoshell SiNS-9 having an average particle size of about 30 nm to 40nm. FIG. 12D is a photograph of aqueous solutions of the pre-taggedsilica nanoshells (from left to right) SiNS-2 (left, suspension inwater), tagged silica nanoshells SiNS-8 (middle, solution in water),water (right, provided for reference). FIG. 12E is a photograph of avial containing SiNS-8 as a lyophilized powder.

Controlled Release.

The following examples demonstrate that if the dansylated silicananoshells have a thin silicon-containing shell (20 nm particles),porphyrin can leak out of the tagged silica nanoshells, whereas if thesilicon-containing shell is thick (30 nm particles), the porphyrin dyecan be retained.

Example 21 Preparation of Dansylated Silica Nanoshell, SiNS-11

The above described procedure for SiNS-2 was used to prepare theprecursor silica nanoshell using extended reaction time to control thenanoshell thickness. The precursor nanoshell solution was solventexchanged with dichlomethane via dialysis (MWCO=14 kDa) againstdichloromethane before dansyl chloride (0.2 g) and triethylamine (0.2mL) were added. The reaction solution was stirred at room temperaturefor 24 hours before being purified by dialysis (MWCO=15 kDa) againstMeOH and then water. The nanoshells SiNS-11 had a diameter of 30 nm, asshown in the TEM of FIG. 13A.

Example 22 Preparation of Tagged Silica Nanoshell, SiNS-12

The above described procedure for SINS-11 was used to prepare SiNS-12using a reduced reaction time to control the nanoshell thickness. TheSiNS-12 nanoshells had a diameter of 20 nm, as shown in the TEM of FIG.13B.

SINS-11 and SiNS-12 were dialyzed against water (MWCO=14 kDa) for 72hours. The absorption curves of FIG. 13C show that a shell thickness of30 nm (SiNS-11) released almost no porphyrin dye (retention of peak at420 nm), whereas the 20 nm shell thickness (SiNS-12) releasedsubstantially all of the porphyrin dye (loss of peak at 420 nm).

III. Preparation of Iron Oxide Nanoshells.

Iron oxide (Fe₃O₄, 6 nm) nanoparticles were synthesized from the thermaldecomposition of iron(III)acetylacetone in benzyl ether in the presenceof oleyl acid and oleyl amine, and the surfactant stabilized iron oxidenanoparticles were isolated by precipitation into hexane, as describedby S. J. Sun et al., J. Am. Chem. Soc. 2004, 126, 273.

In a general procedure, a solution of the appropriate star polymer (20mg), a hydrophobic porphyrin dye (2 mg) and the surfactant stabilizediron oxide nanoparticles (10 mg) were dissolved in THF (0.2 mL) andstirred at ambient temperature for 30 min before the solution wasrapidly injected into water with rapid stirring. The aqueous solutionthus formed was filtered though a 0.2 micrometer teflon filter andfurther purified by centrifugation.

Example 23 Preparation of Iron Oxide Nanoshells SPIONNS-1

The above described procedure using star polymer SP-1 was used toproduce an iron oxide nanoshell SPIONNS-1 in water. FIG. 14A is a TEM ofSPIONNS-1. FIG. 14B is a pair of photographs of SPIONNS-1 as an aqueoussolution having a rust orange hue (left) and a brown colored lyophilizedpowder (right). The solution has UV-VIS peaks at 420 nm and 550 nm, andemission peaks (for excitation at 420 nm) of 650 nm and 720 nm, as shownin the absorption curve of FIG. 14C.

Without being bound by theory, it is believed that the self-assemblyprocesses producing the occluded dye component and the shell componentcan be effected in tandem. The hydrophobic dyes are held inside the starpolymer to form an occlusion complex wherein the polymer structureshields the dye to some extent from the external environment.Additionally, the iron oxide nanoparticles are believed to be bound tothe periphery of the polymer to form a nanoshell which to some extentshield the polymer from the external environment.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. When a range is used to express apossible value using two numerical limits X and Y (e.g., a concentrationof X ppm to Y ppm), unless otherwise stated the value can be X, Y, orany number between X and Y.

The description of the present invention has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiments were chosen and described in order to best explain theprinciples of the invention and their practical application, and toenable others of ordinary skill in the art to understand the invention.

1-40. (canceled)
 41. A nanoshell, comprising: a star polymer occlusioncomplex comprising i) an amphiphilic unimolecular star polymer having acrosslinked core covalently linked to 6 or more independent polymerarms, and ii) a cargo material occluded in the star polymer; and a shellcomprising gold in contact with a peripheral surface of the star polymerocclusion complex.
 42. The nanoshell of claim 41, wherein i) the core ishydrophobic, ii) the cargo material is hydrophobic, and iii) each of the6 or more polymer arms comprises a) a hydrophobic chain segmentcovalently linked to the core and b) a peripheral hydrophilic chainsegment linked to the hydrophobic chain segment.
 43. The nanoshell ofclaim 41, wherein the shell comprises one or more shell layers.
 44. Thenanoshell of claim 43, wherein the one or more shell layers are porous.45. The nanoshell of claim 41, wherein the nanoshell has an averagediameter of about 15 nm to about 300 nm.
 46. The nanoshell of claim 41,wherein the cargo material is an imaging agent.
 47. The nanoshell ofclaim 41, wherein the cargo material is a biologically active compound.48. The nanoshell of claim 41, further comprising an organic surfacegroup covalently linked to the shell, the organic surface groupcomprising a chemical moiety selected from the group consisting of dyes,poly(alkylene oxide) chain segments, poly(alkylene imine) chainsegments, biologically active moieties, and combinations thereof. 49.The nanoshell of claim 41, wherein an aqueous mixture of the nanoshellis suitable for diagnostic imaging.
 50. A method, comprising: treating astar polymer occlusion complex with gold seeds, thereby forming a seededocclusion complex, wherein the star polymer occlusion complex comprisesan amphiphilic unimolecular star polymer and a cargo material occludedtherein, the star polymer having a crosslinked core covalently linked to6 or more independent polymer arms; and depositing gold by electrolessdeposition on the seeded occlusion complex, thereby forming a nanoshell,wherein the nanoshell comprises a shell comprising gold in contact witha peripheral surface of the star polymer occlusion complex.
 51. Themethod of claim 50, wherein i) the core is hydrophobic, ii) the cargomaterial is hydrophobic, and iii) each of the 6 or more polymer armscomprises a) a hydrophobic chain segment covalently linked to the coreand b) a peripheral hydrophilic chain segment linked to the hydrophobicchain segment.
 52. The method of claim 50, further comprising treatingthe nanoshell with an organic tagging agent, thereby forming a taggednanoshell comprising an organic surface group covalently linked to theshell, the organic surface group comprising a chemical moiety selectedfrom the group consisting of dyes, poly(alkylene oxide) chain segments,poly(alkylene imine) chain segments, biologically active moieties, andcombinations thereof.
 53. The method of claim 50, wherein the starpolymer is formed by organocatalyzed ring opening polymerization. 54.The method of claim 53, wherein the star polymer comprises apolycarbonate chain segment, a polyester chain segment, or a combinationthereof.
 55. The method of claim 50, wherein the cargo material is animaging agent.
 56. The method of claim 50, wherein the cargo material isa biologically active compound.
 57. The method of claim 50, wherein thenanoshell has an average diameter of about 15 nm to about 300 nm.
 58. Ananoshell, comprising: a star polymer occlusion complex comprising i) anamphiphilic unimolecular star polymer having a crosslinked corecovalently linked to 6 or more independent polymer arms, and ii) a cargomaterial occluded in the star polymer; and iron oxide in contact with aperipheral surface of the star polymer occlusion complex.
 59. Thenanoshell of claim 58, wherein i) the core is hydrophobic, ii) the cargomaterial is hydrophobic, and iii) each of the 6 or more polymer armscomprises a) a hydrophobic chain segment covalently linked to the coreand b) a peripheral hydrophilic chain segment linked to the hydrophobicchain segment.
 60. The nanoshell of claim 58, wherein an aqueous mixtureof the nanoshell is suitable for diagnostic imaging.
 61. A method,comprising: forming a mixture containing an amphiphilic unimolecularstar polymer, a cargo material, and iron oxide in a suitable solvent,the star polymer having a crosslinked core covalently linked to 6 ormore independent polymer arms; and injecting the mixture into a secondsolvent, the second solvent being a non-solvent for the cargo material,thereby forming a nanoshell comprising the star polymer, the cargomaterial, and the iron oxide.
 62. The method of claim 60, wherein i) thecore is hydrophobic, ii) the cargo material is hydrophobic, and iii)each of the 6 or more polymer arms comprises a) a hydrophobic chainsegment covalently linked to the core and b) a peripheral hydrophilicchain segment linked to the hydrophobic chain segment.
 63. The method ofclaim 60, wherein the nanoshell has an average diameter of about 15 nmto about 300 nm.
 64. A tagged silica nanoshell, comprising: a starpolymer occlusion complex comprising i) an amphiphilic unimolecular starpolymer having a crosslinked core covalently linked to 6 or moreindependent polymer arms, and ii) a cargo material occluded in the starpolymer; a shell comprising silica in contact with a peripheral surfaceof the star polymer occlusion complex; an organic surface groupcomprising a poly(alkylene oxide) chain segment covalently linked to theshell; wherein an aqueous mixture of the tagged silica nanoshell issuitable for diagnostic imaging.
 65. The tagged silica nanoshell ofclaim 64, wherein i) the core is hydrophobic, ii) the cargo material ishydrophobic, and iii) each of the 6 or more polymer arms comprises a) ahydrophobic chain segment covalently linked to the core and b) aperipheral hydrophilic chain segment linked to the hydrophobic chainsegment.
 66. The tagged silica nanoshell of claim 64, comprising asecond organic surface group covalently linked to the shell, the secondorganic surface group comprising a chemical moiety selected from thegroup consisting of dyes, poly(alkylene imine) chain segments,biologically active moieties, and combinations thereof.
 67. The methodof claim 64, wherein the tagged silica nanoshell has an average diameterof about 15 nm to about 300 nm.
 68. A method, comprising: treating astar polymer occlusion complex with a first tetravalent siliconmaterial, thereby forming a precursor silica nanoshell, wherein the starpolymer occlusion complex comprises an amphiphilic unimolecular starpolymer and a cargo material occluded therein, the star polymer having acrosslinked core covalently linked to 6 or more independent polymerarms; treating the precursor nanoshell with a second tetravalent siliconmaterial comprising a nucleophilic group, thereby forming a silicananoshell comprising a shell, wherein the shell comprises i) silica incontact with a peripheral surface of the star polymer occlusion complexand ii) nucleophilic surface groups selected from the group consistingof amines, thiols, alcohols, and combinations thereof; covalentlylinking to a nucleophilic surface group of the shell an organic surfacegroup comprising a poly(alkylene oxide) chain segment, thereby forming atagged silica nanoshell; wherein an aqueous mixture of the tagged silicananoshell is suitable for diagnostic imaging.
 69. The method of claim68, wherein i) the core is hydrophobic, ii) the cargo material ishydrophobic, and iii) each of the 6 or more polymer arms comprises a) ahydrophobic chain segment covalently linked to the core and b) aperipheral hydrophilic chain segment linked to the hydrophobic chainsegment.
 70. The method of claim 68, further comprising covalentlylinking to the shell a second organic surface group comprising achemical moiety selected from the group consisting of dyes,poly(alkylene imine) chain segments, biologically active moieties, andcombinations thereof.